A gay friend of mine one said he hits on straight guys because "occasionally, it works." I have myself hit on lesbians over the year, banter is banter, to various degrees of success. This doesn't really have anything to do with the opening scenario, as the person in question isn't trying to trick anyone, they feel like they are a woman and want to be in a "heterosexual relationship," as a woman.
I am a happily married heterosexual man, but I was talking with some of my buddies from college and realized I may have briefly been involved with a transgendered woman. My sophomore year of college (way back in 2003) I was messing around with a girl that was in my art history class. We got together a few times, drank and fooled around, and here are things I didn't think about AT ALL until just a year or two ago.
1.) She was a cute, petite Asian girl, so I didn't think anything was out of place. She did have fake breasts, though, but that's not super uncommon, right?
2.) She didn't want me to go below the waist, always kept her pants/shorts on, but, like I said it was brief... we only hung out for around 3 weeks.
3.) She said some weird stuff when drunk. First, she said, a couple of times, that she didn't always look this way. I think there may have even been some talk about her parents paying for her to look that way.... but I thought that might be tied into the fake breasts.
4.) One time we were drunk she kept asking me was if I was even a little bit gay.
So yeah, that's that. If she was born a man and I we had continued fooling around? Can't really say what I would have done. Probably would have stuck around, I'm straight because I'm attracted to women and not men, and I was attracted to this person.