Hi Emerald
Welcome to Susans. Glad you found us. You are among Kindred spirits and I hope we can help you find the answers to you questions. I tracked down your first post about your partner. My heart goes out to you firstly as you seem to be hurting quite a bit. I hope you can find a way through this for your families sake.
I wanted to address some of the things you bought up in your post as best I can.
Quite often when we are first starting to work out whether or not we are transgender things that have happened throughout our lives that didn't make sense now begin to fit in a way they never did before. Some trans women will say things like "I always knew I was different" or I always knew I should have been born a girl" and then there are others who don't really have a clear idea of what is going on. It can take many years for them to work out what it all means for them. What many of them will do is go to extraordinary lengths in order to hide their feelings or even over compensate by doing really macho type activities. For many as they progress through the years they take extreme risks and show a real lack of care about their own wellbeing...all these behaviours are typical but not essential to being trans.
Sex and gender are two different things but for most people they align however not always. As the saying goes
"Sex is about who you go to bed with, Gender is about who you go to bed as."
He may well be at this stage, a bit self absorbed in his new found freedom, being able to express himself and know that he will not lose you. This for many of us in relationships is the most frightening and confusing part. I hope he will work out fairly quickly what is important to him, but for many it takes time. Dena suggested a therapist and from my personal experience I also think that it is a great idea. You need to take care of you as much as he needs to work out what he wants so you may want to consider one for yourself.
Dysphoria is a tricky thing which can take some time and a professional to sort out. He does not have to have Dysphoria to be trans but he may not recognise it for what it is. I am not sure about the sexual fantasies and can only speak for myself. I personally did not realise how much I did fancy guys until I began to transition and was honest with myself. However that attraction is not enough to destroy my 33 year marriage. I love my wife too much to give that up for some fleeting sexual encounter.
You may well find that things settle down after the initial period of excitement. I know for me it was a huge relief to know that my wife was not going to leave me. What that meant was I had to work at making sure I looked after her and what she needed in the relationship if I was to make it work for both of us. If he wants to have HRT, he is likely (depending on where you live) to have to see a psychiatrist in order to begin in the first place. This may also be a good opportunity to examine what he really wants.
I wish you luck and hope that you can keep your relationship going. That you have come here seeking help for you both shows just how dedicated you are to keeping your family intact. He would probably benefit from thinking about how he would feel if you came out to him as FTM (female to male). It was said to me early on in my transition that when one person transitions the whole family transitions.
If you have more specific things you want to ask please feel free I am only too happy to try and answer them for you if I can.
Take care
Liz