Hi, Dana. I, too, have apprehensions about staying in my relationship. My issues seem fairly simple on the surface: I identify as a gay boy, and I'm not sure I want to be with a straight man for what might be the rest of my life. I'm not simply preoccupied over the label; there's more to it than that. Once my physical transition is well underway, I'm not sure how my partner will relate to me or how I will relate to him--both sexually and socially. Then I have to cope with his misgivings; he quite emphatically does not want to be perceived as a gay man. I can well understand this; for years and years, I have deeply resented being seeing as a straight woman instead of the gay guy that I felt I was.
Unfortunately, there are many complex issues for me to deal with that I'm afraid will influence me in unhealthy directions--perhaps to stay with my partner when that isn't the best choice. For instance, I still haven't finished grad school (I'm not a student anymore, but I haven't finished my dissertation). I have delayed working on my diss while I cope with my trans issues, and I don't know whether I could work on it if I were adjusting to a single life after almost two decades of being with my partner.
I also don't have a stable job (I teach at the uni where I got my master's, but I'm only hired on a per-term basis and have no job security). When I am working, it's usually not full time these days, and even if it were full time, I wouldn't make half the income that my partner makes. So money is a consideration. I don't want it to be, but it is.
And, as I said, we've been together for nearly two decades. That's a long time. We care about each other, and we are used to each other.
I fully expect to work through all of this junk with my truly phenomenal therapist, but I, too, have not encountered very much press about this phenomenon. Mostly it's the significant other who is under the magnifying glass, with the trans person being the one who hopes and prays that the SO will stay in the relationship. But I don't think it should be surprising that you are having these feelings. Because I'm experiencing something similar, I'm usually kind of surprised that other trans folks don't say anything about feeling the same way. Of course, a lot of the trans people I know were single already, but I'm talking about people who definitely were in relationships when they came out or decided to start transition.
My therapist told me that I should not mention to my partner that I am having ambivalent feelings about him, and I think that he is right--for me, at least. I need to work through the ambivalence in therapy before I ever suggest to my partner that I am having second thoughts about our staying together. This approach might not work for you. But I urge you to talk to your therapist about your feelings if you haven't already.
I hope it helps you some to know that you're not alone.