I know it's cliche, but I think the BEST thing about the typical bisexual support is the idea of dating and loving a person FOR BEING THEM!
You could obviously date other guys, even other trans guys! But you sounds very much into THIS particular, special dude and it sounds like you would like him if he were cis too. Certainly there are very specific problems for trans and genderqueer people and anyone who can't easily fit into a label or box of whatever kind. His personality and life experiences have made him the person you want to be with. It really sounds like you love him as a whole, not IN SPITE of him being trans. He makes you feel good and it sounds like you do the same for him- maybe so much he feels guilty for 'wasting your time'. It's okay to tell him your feelings, you can even say gently that at first you were a little surprised or unsure- honesty is part of good communication if you are doing it with care. But both of you should know that EVERY human comes with strings, issues and emotions. You can remind him that you have flaws too, if you two have ways of working things out, remind him that every couple that was ever successful and still in love has had to figure out how to deal with one another in one way or another. You sound very caring and non-judgemental and all you can do is express these things as best you can. If you were dating someone else you would miss a lot of things about your special guy! If you have to write it down to make it clear, I love the idea of a letter or email as something he can have even when you aren't around.
I still have the email from my parents when I emailed them about being transgender and it still makes me cry like a big gooby dork and really little else these days does that aside from my friends and family being super awesome and loving. You can't fix his insecurity, but there's way to express that you aren't missing out on anything. I am a transguy that appreciates cis men, I am attracted to them greatly, but really the body/bio maleness is just a different flavor icing on the cake when your friend and lover is wonderful person that you want to share your life with. You two are both very brave people to just live your lives, but by no means are you compromising yourself by choosing him over a cis-male! He may not be able to change his thoughts about it overnight, but there are people out there like Dan Savage who will very happily and aggressively assert that there is not better than less than when it comes to a loving relationship as far as queer/straight/trans/cis/bi/poly/asexual whatever someone's personal deal is. Being trans (or different in many other ways) can be extremely isolating and painful but it can create an extremely unique perspective of the world that few are lucky enough to understand or learn about.
" I was a little shocked and confused with my own feelings toward him, but in my eyes him being trans didn't change my feelings for him and decided to see where it would lead. Now looking back, I can't believe how nervous I was. He is one of the best things that has ever happened to me. I am so happy and I see a long future with us together." You can pretty much say exactly this in a little more intimate terms... No amount of outer love can fix the self-loathing, no matter what pop love songs tell us, but it can really help someone see that they are safe and okay to be themselves. I have my own lame moments of self doubt and it's a terrible burden for anyone to bear, for any reasons.
If you think it's something he'd be willing to try, you might be able to join PFLAG or some kind of local queer or trans union. A group of similar people, couples or otherwise could maybe help you both feel more connected and accepted? Even just being on forums like this helps my peace of mind a lot on bad days!
