It's been said.

Last night, I finally got her to talk to me. I guess she didn't realize she was shutting me out so much, but she was. I asked her, "Ok. Talk to me. What's going on?" "Well," she said, "I'm transgendered." Ok. It's one thing to know it... It's another thing to hear it. I'm having a hard time allowing myself believe it. I feel like it's just going to go away... even though, of course, I know it won't. I think we're going to be ok. She says we need to just take it a day at a time. I'm helping her pick out a male name. I won't use masculine pronouns until she has a male name. This all feels so weird.

http://www.forge-forward.org/handouts/Transpositioned.html

FTMs often say that they've always been male; they're just making some physical and/or social adjustments so that other people recognize that fact. That's not how a lot of lesbian partners see the process. Although many always saw and often much appreciated their lover's butchness, they say what they prize is masculinity wrapped in a woman's body; masculinity as displayed by a man often feels totally different. One woman commented about a photograph in Loren Cameron's seminal FTM book, Body Alchemy: Transsexual Portraits (Cleis Press, 1996), showing Loren with his butch lover: "The picture of Kayt and Loren arm-wrestling struck me because the line where their hands met is the line of my desire. Kayt is totally my type. Transgendered, male-identified in a woman's body." Another responded to a discussion about the sexiness of butches: "I know what you mean about the attractiveness of that look in a woman that says, 'Don't fuck with me,' but the same look in a guy feels threatening and dangerous because society has ingrained that in us through years of oppression and violence towards women. Thinking of my lover as a 'man' reminds me of the mean men in my past." Some know why this memory of past mean men is an extremely scary proposition: "I am also a survivor of sexual abuse, mostly at the hands of men, and I am afraid of how my partner's transitioning might trigger me." Others can't articulate the source of their fear, but know that it's there: "I just get nervous thinking about being in bed with a man."
...
Lesbian-identified partners also worry about how their own identity might change. It's easy to define yourself as a lesbian when everyone can see that your partner is a woman. When your partner is a man, however, even a strongly-held sexual orientation identity of "lesbian" may seem less defensible. One woman said, "I'm very dyke identified. The possibility that he might transition and 'become male' scares me because I feel like my identity hangs in the balance." A self-described femme echoed that feeling. "I'm really wary of giving up my identity for someone else. That seems like such a stereotypical femme thing to do -- 'it's o.k., honey, your identity is more important than mine.'" On the other hand, insisting on a lesbian identity when one has an FTM lover may feel like an undermining of his right to self-define: "I can't in good conscience call myself a lesbian and validate his gender identity when he isn't identifying as a woman," one woman explained.

I do feel as though my identity hangs in the balance. It's a ridiculous thought that my identity depends on another person. When I had never been in a relationship with a woman, my self-proclaimed identity as a lesbian was ignored, even laughed at. I bounced between the identities of lesbian and bisexual because I couldn't deny the attraction to men. Though I am certain that my attraction to women has always been strongest. The men I was attracted to were decidedly the more feminine in my peer group. However, the women I have been attracted to (in more than a mere fantasy setting) have been butch. I feel as though I may be attracted to androgyny. I fear that my lover will move from her sweet, soft, handsome self to the rough man I've always avoided.