Hi, and welcome!

I'm 45 and I
know I'm FtM; I started my transition at 40. As you can see from my ticker I've been on T for more than 3 years, and I had top surgery 3 years ago. I've struggled with my gender since age 5, and I can relate to a lot of what you've posted.
Ok, introductions aside: let's look at your post point-by-point:
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
I kept it to myself, yet I soon found that I couldn't.
Yup, Gender Dysphoria is like that. You notice it, then it builds & builds, then it becomes overwhelming to the point where you have to do something about it. It's possible to distract yourself from it but it
never goes away on its own. You're experiencing what a lot of us have experienced: as soon as you accept that you have issues with your gender, you find that your appetite to change certain things in your life increases until you get to the point where you're comfortable. The most difficult bit is the bit between accepting your own trans status, and getting to the place you need to be.
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
I almost lost my boyfriend of three years over this, but he has since promised to stay by my side.
Sadly, it's unlikely that this will happen in the long term, as I'll explain in a bit.
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
I'd be devastated if I lost him, and my mom uses my relationship with him to insist that that means I must be confused (because I'm apparently not gay, according to her).
Your mother's grasping for reasons why you could be feeling this way. She does that again further down in this thread. This is part of the 'denial' phase of grief: I daresay she loves you and wants what's best for you; what loving parent would want their kid to have a more difficult life? So she's desperately searching ways for you to just be a straight girl, because she knows that that's the easier option. Or so she thinks. You see, it's only easier if you
are a straight girl. If you aren't then it's torture.
Y'know, I went into denial for 21 years after I first realised I needed to transition when I was your age. I convinced myself that I couldn't be trans because I'm attracted to men, so surely that must mean I'm a woman, right? Surely it'd be easier for me to continue living as a woman because then I could choose from a huge pool of straight men rather than a tiny pool of gay men. Right?
Wrong. It's amazing what we can make ourselves believe if we desperately want to believe in something. Spending all those years trying to figure out how to live as a woman was like Chinese Water Torture: every single day of seeing a body I hated; being treated like a woman when it feels so very unnatural; even being treated like a woman in bed was a constant torment to me.
Of course it's possible for you to be gay. Trans people come in all sorts of sexualities, and two-thirds of us are either gay or bi/pan.
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
For some context, I wasn't your typical child that you see in a classic FTM case that screams "how didn't I see it?". I played with Barbies and such as a child, but one of my favourite things was animals. I had an army of stuffed animals that I would play doctor with and I would come up with stories for them. Dress-up was another favourite, but I would wear my knight armour just as often as I'd put on the dress. I was always about comfy clothes over looks.
How is this not typical? It's actually very typical, but what you mean is that it's not
stereotypical. There's a stereotype of what an FtM kid is supposed to be like, but like most stereotypes it only has a very loose connection to the truth. I played with Barbies & Cindy dolls; I loved animals and considered becoming a vet; I had 3 (count 'em - 3!) Pink Panthers that I adored as well as a host of teddy bears etc. I also loved dress-up: I tried dressing up in my mother's clothes but that didn't really work out for me; I far preferred wearing boys' clothes but that simply wasn't acceptable in the 1970s. I'd far rather be Superman, Buck Rogers or Steve Austin than some princess.

Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
This all sounds fine, until you add in the factor of my social life. I was frequently excluded by my peers (especially by the "popular girls". One of them was a friend of mine outside of school only and it crushed me when she rejected me at school to hang out with the popular crowd.) This rejection and being "fringe" has continued my entire life. I always seemed to find the weird kids to be friends with, not that I minded.
Same! The weird kids are way more fun to hang out with than those sycophantic popular kids anyway.

One of the big problems we tend to have is this: girls are (typically) very social creatures. They're highly sensitive to how well other people fit in with their cliques, and if they detect that someone isn't quite their kind of person, they can be vicious or even cruel. I had the same experience as you: I was forced to hang out with girls because where I was brought up it wasn't acceptable for girls & boys to play together. The more popular girls instantly picked up on my relative social awkwardness, and they made sure I knew exactly how they felt about it.

Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
My mom believes this rejection from the "pretty, popular girls" encouraged this to happen to me.
If that were true, then
every socially awkward, bullied girl would turn out to be transgender. Which is patently not true! Every class has a couple of socially awkward girls who tend to get picked on, but how many of them turn out to be transgender boys? There you go.
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
Additionally, my grandmother lived with my parents for the majority of my childhood, and she wasn't the most mentally-well. She has an amazing ability to rewrite the truth and genuinely believe it, so she and my mom would get into wicked arguments. My mom has also been depressed for the past eight years has only started recovery last year. In short, my dad cheated on her (and she cheated on him eight years earlier, leading to her depression) and it lead to them separating but remaining in the same house. It was a hellish year as I navigated choosing which university I wanted to go to and such while they would scream at each other late into the night. They have made up and are doing much better, but last year still haunts all of us. My mom believes that it was this last year of trauma that brought this on. It's another possible factor I have trouble ignoring.
Sounds like your home life has been hell on wheels for the past few years. Sorry to hear that. However, millions of kids around the world grow up in similar - and far worse! - situations, and how many of them are transgender? Exactly. This is your mother clutching at straws again, trying to sow doubt into your mind so you won't do something she considers to be detrimental to you.
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
I would probably have an easier time accepting all of this if I wasn't Christian. Now, before you get the wrong idea, I'm quite liberal in my views. (This is exactly why I hate calling myself Christian.) I've been in fandoms since early high school, and the introduction of shipping as well as having friends come out to me forced me to reconsider what I believed about LGBT+ stuff. Now, I can fully say that I support same-sex marriage and trans identities and I still believe in God. I've also been accepting the idea that He could have made me trans for a reason I can't understand, so that helps. Part of me questions if I never considered the possibility of being trans when I was younger because of my upbringing. What if being raised Christian prevented me from seeing it about myself?
Hooray for fandoms! So glad your ships are helping you see the light.

Yes, it's entirely possible that being raised as Christian meant that you were given some very strict guidelines about how a good Christian child should behave, and that you spent many years interalising those messages. I too was raised Christian until I discarded it; some of those teachings are unnecessarily restrictive and I'm so glad to be free from them. It's good that you're starting to discard some of the more harmful teachings.
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
I got a binder from my university, and I really love having a flat chest. I have thought of top surgery and would joke about having my boobs cut off when I was in puberty. I only wear sports bras when I'm not binding because I almost cried when I tried to wear a normal one. I've never really liked having boobs.
Women don't say this. They might say that their chesticles (I dislike the 'b' word) get in the way; or that they're annoying; or that it sucks when they hurt once a month. But they never say they'd be happy to get rid of them. On the contrary: most women see them as an innate part of their identity & they would be utterly devastated if they had to lose them.
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
I've also had my mom buy me men's pants to go with my men's/unisex graphic tees and men's hoodies. I feel good wearing these things until I think I should be trying harder to like being feminine and then I just make myself feel ugly.
Do you feel ugly, or do you feel uncomfortable?
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
This is all appearance stuff, but I also have been called "he" online in video games, and I liked it more than I'd care to admit.
...
I inwardly cringe when I'm called "she" and don't like being called by my full name (my "nickname" is a great neutral name).
Again, this isn't something a woman would say. Women would generally find it offensive if someone were to refer to them as 'he'. If you liked it, it's probably because it felt right. Right? And they don't cringe at being called 'she'. But we do. I certainly did; it would be utterly bizarre for someone to do it now because I don't look or sound like a 'she', but back when it used to happen it felt like a slap in the face every time.
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
I don't care about having a dick; my vagina is okay and I've heard FTM bottom surgery isn't super great.
Um, you may have been misinformed about bottom surgery. It's come on phenomenally in recent years and it can actually be incredibly good now. But I don't mind my 'man cave' either (again, I dislike the 'v' word), not that it matters: your genitals don't define who you are.
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
(Considering I want kids and my boyfriend is straight (and uncomfortable with the idea of being gay),
Aaaand here's the bit where it becomes apparent that your boyfriend is (sadly) unlikely to stay if you decide to transition. If he's uncomfortable with the idea of being gay, that means he's uncomfortable with being seen by other people as being in a relationship with someone who they perceive as being male. That's you, if you transition. He probably loves you, and is happy to stay whilst you appear to be female to the rest of the world... but the instant you do anything to appear masculine (rather than just tomboyish) - such as top surgery or hormones - he's likely to lose interest because he doesn't want other people to think he's dating a dude. Because dating a dude is incompatible with his own identity. I'm so sorry, but if he's straight he is very unlikely to stay if you transition.
I have two kids: I delayed my transition so that I could have them. There are plenty of guys who've done the same, or who have paused their transition to have them. Some have had them after transition. There are options available to you.
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
I also to like painting my nails and wearing some jewlery, so there's also that.
Plenty of guys do this; especially rock stars. Doesn't make them women. As for jewellery: ever seen a pic of Mr T?
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
Yet, (TMI) I find myself more turned on when I imagine myself being a guy when my boyfriend is being romantic with me. I doubt cis women think like that.
Some do; where do you think slash fanfic comes from?

The overwhelming majority of it is written by heterosexual women, with a tiny minority of stories being written by gay men. But yeah, this isn't uncommon for FtM guys too: of course it's only natural for us to picture ourselves in a male role when in TMI situations. The difference is: once you transition, it becomes a reality rather than a fantasy.

Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
I also did go to a gaming convenion with him recently and, with the event being 98% men, I wished to be seen as a man too and not one of the ten or so women there. Generally, I feel like there may be something there but I have doubts yet again.
Those doubts are perfectly natural. Transition is a huge undertaking, and there's a lot to consider. We've all had some doubts along the way; if you hadn't had any doubts that would mean you weren't thinking it through properly. I had doubts too, and used them to delay my transition by 21 years. Didn't make me any less trans though.
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
I have considered if I'm non-binary. I've thought about neutrois or the like, but it didn't seem to bit. I considered demiguy but, well, SJWs are the bane of my existence.
Don't get hung up on labels - just be you. If 'he' fits better, you're 'he'. If it takes you a couple of years to work through your gender identity to settle on exactly where you stand, that's absolutely fine. You don't need to pick a label or a tribe just yet. Take your time.
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
My depression is caused by my gender identity issues as well as the rejection from my past. My self-esteem is rather poor. So, I often get down when I feel dysphoric and when I doubt myself. I am in counselling and my counsellor knows about my gender issues.
Bingo! A lot of this is familiar. It's enormously common for trans people to feel depressed before we transition. That type of depression practically evaporates once the world sees you correctly. The rejection issues & self-esteem are another matter (they don't automatically evaporate) but it's easier to work on them once you've got your gender issues sorted out.
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
If you have any ideas about how I can find out whether this is legit or not, I would really appreciate the help.
Only you can know whether you're trans. But the best way to come to your own conclusions is to discuss this with a qualified Gender Therapist. So find one near you (or online), and start exploring.
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
I just want some input to see if this sounds like it's real or if it's just a symptom of poor self-esteem.
Sounds very real to me! It's certainly real enough to discuss with a Gender Therapist.
Quote from: CorporalFire on March 07, 2017, 12:57:48 AM
Also, if you have tips about how I can help my boyfriend, that would be great. I just want to make this easier on both of us.
Be honest with him, and keep that honesty going - even if you're scared that he might walk out on you.
You deserve your own happiness, and you deserve the right to be yourself. You cannot live your life for your boyfriend so don't base your decisions on what he wants. However, he also has a right to decide whether he wants to continue being in this relationship, so make sure you keep him informed of your plans. If he does walk out, he wasn't right for you in the first place.