This sounds far more of a gender thing, how you see yourself, how you feel about yourself, relationship dynamics with regards to your gender...

A woman who is butch doesn't necessarily see herself as not female, just that she doesn't associate with or present herself as stereotypically female. I would be concerned about how it might cause problems even to an openminded lesbian if you were to be called her boyfriend- that is to say, if she calls you a boyfriend it might be a little challenging to her perception of her own orientation (I only say that because I heard of a pre-op transguy having problems with his girlfriend like this) and she would be attracted towards you as a woman, which might cause a problem if you wanted to be seen as male or actually even transition in the end.

You say your best option for a feminine guy-girlfriend would be a gay guy, but you'd also run into the problem that he wouldn't be sexually attracted to a female body (although he might be willing to engage with it if you outwardly presented as male). I wonder if you might find it beneficial to go onto a gender website, where you might be able to work through how you feel about your own gender and perhaps even find some transwomen there who are pre- or non-op who would look male but be happy to be a girlfriend, if you see what I mean.