I have another perspective from being somebody who transitioned while married a ways back and how life is now. When I first started out on my journey, my wife was very supportive of me...at first. After she had time to process the implications and that transitioning costs money, she started pulling away from me. She was also afraid I would want to be with a man, though in the end I'm definitely on the lesbian end of the spectrum.
I continued transitioning and went full time about 8 months after coming out to her. Eventually, after she started treating me badly and I've since come to realize she was emotionally abusive, I separated from her and moved out. About a year and a half later we were divorced. The divorce happened about 8 years ago, so it's been awhile.
After we separated I actually felt so free. I stayed single for a few months, but I wanted to explore my sexuality and I started dating various people including a post-op trans woman (who's currently still my best friend), a couple guys, and several women. At that point, I realized I was pretty sure I wanted to be with a woman and I had a good idea of what I wanted in a partner. I joined a lesbian choir (still somewhat involved with it) and met my current partner about 5 years ago. She was exactly what I wanted in a partner and she completely loves me for who I am. To be honest, I'm happier with her than I ever was with my wife. Now that gay marriage is legalized, she proposed to me about 4 months ago and we're engaged and I have my surgery scheduled for next year.
My point is, even if your current marriage doesn't work out, it may be for the best. While it does take a special person to stay with a transgendered person, the strain it can cause on a marriage may make the relationship untenable for either of you and sometimes it is better to move on to something that makes both people happier.