Hi Jocelynn... a friend told me about your post. We're in the exact same situation, so much so that my friend thought that this post was written by me.
There is a bit of difference in that I'm transsexual. I transitioned young and, today, live my life no different from any other girl (I like to think so anyway). I've never had any interest in dating a transperson; I like my men, men... period. So I met this guy about three years ago, we met through a mutual friend. He says it was love at first sight for him. He started showing interest and telling my friend he wanted to date me. She takes it upon herself to tell him about me. After some time he finally came to the conclusion that he fell for the girl he met and wanted to start a relationship. For girls like me, it really was a dream come true.
Well, to make an already long story short: As the days turned to weeks and weeks turned to months, I started having these suspicions. I started to constantly ask him if there was something he needed to tell me, hinting at something gender related. He vehemently denied anything. I started to feel like he was somehow living vicariously through me. It really bothered me. Then he started expressing that he wants to dress more "stylishly," or something to that effect. Well, here in Los Angeles, that can mean some pretty far out things. He kept saying how black nail polish is cool and blah blah blah. It honestly grossed me out. I wanted a MAN; it was just my preference but I also wanted to be the "good girlfriend" that sticks by her man. I pride myself in being accepting of other people's lifestyles, interests and preferences. I felt so guilty that I was so disgusted by how my boyfriend was presenting himself. Now, trust me, I have plenty of friends who express themselves in random ways... but I wanted MY boyfriend to be a guy... not anything "in between." I kept asking if there was anything different he felt as far as gender. He always promised no.
So anyway, here we are three years later. We actually started having problems that, at the time, seemed unrelated to all this (in hindsight, this "issue" had a role in all our problems) we ended up breaking up about two months ago; not long after, he told me. I took it hard. Look, we're entitled to our preferences. I don't judge him for wanting to go through with what he's doing. I even feel so bad for him that he had to experience this his whole life. That's so awful and I don't wish that upon my worst enemy. But I want a man. In the three years we were together, I gave him every opportunity to come clean. We were supposed to have this amazingly honest relationship -- and I was. He lied for three years whether he "came to terms with this" or not, in the end -- it was a lie. In the end, he has to do what he needs to do to make himself happy. I think we all have to be happy with ourselves before we can be happy with others but I'm mad as hell.
I was lied to and now, I'm just collateral damage. He wasted three years of my life trying to figure himself out. I'm glad he did, but I got the big F--- you. I sympathize for transsexual women; hell, I empathize with them. It's HARD to live that lie, so on that level, I wish him all the best. On a personal level, I don't want a boyfriend that becomes my girlfriend. That's way too out of my league of acceptance. He wanted to stay together, but I couldn't be more repulsed by the thought of the man I gave myself to wanting to become a girl. It's not a broad "transsexual issue," it's a personal one between me and my "boyfriend."
I guess what I'm saying is: you're entitled to how you feel. It doesn't make you a bad person by not wanting this out of your relationship. You're entitled to being happy and spending your life with exactly who and what you want as much as "he/she" does (that isn't meant to be derogatory, I'm just not sure how to address your SO as to not make you uncomfortable). If you stick around... you're a better person than I. If you leave and you two remain friends... your parents raised a wonderful person. If you leave and you're mad as hell... you're normal.
Take care, good luck... this is difficult for all parties. The important thing is: you're happy.