Boyfriend seems to be interested in gender transition

Disregarding all the other aspects I have what some might call a stupid ignorant question... If he decides to transition to female, and I choose to stay with him...would that make me a lesbian by definition?

This isn't even a conversation we've had yet, I've just found out two months ago that he's bi and then a few nights ago that he was researching gender transition. I haven't brought up the gender transition research to see if this is something he's curious about or truly interested in...but nonetheless, now that I know, it makes me wonder if being with a gender transitioned person would change my orientation by default. Yes, I know, I sound stupid and ignorant but I'm just lost and confused and questioning everything right now...