What do you consider a gay relationship?

I just ran across a post where a couple claimed to be gay but I simply cannot understand how. The circumstances were as follows.Woman (who identifies/lives as a man but has not had any surgery of any type)Man (Who claims to be gay)I mean if I were a gay man I can only assume I would want to be with a man and have sex with a man. As all my gay male friends do. If I were a woman who was gay I would want to have sex with women, even if I started living as a man. If a man and woman have sex as a straight couple do - how is it possible they are now gay? I have tried figuring it out and simply cannot for the life of me. If a man is married to a woman and decides to grow his hair out and put on lipstick surely they aren't lesbians all of the sudden.Thanks for any insight/thoughts you can provide.