Best friend wants to be a woman.

Dear FutureMe, K still intends to be a woman. I want to stop him because I have a bad feeling about it turning out bad for him, but he's at the point that he can't be convinced. His alleged feelings for me are also a factor. I don't believe he's lying about it, but at the same time, I don't know how deep these feelings are. What's worse is he seems to have a lot invested in these feelings. I can't really see my feelings for him as a best friend turning into feelings for him as a lover, regardless of gender. But by rejecting these feelings, do I cause him harm that he may not recover from? Or affect us in a way that we can't be friends anymore? I wish I could get him to not take this path. Especially since it's not something he can undo. I'll keep supporting his choices. I just want a happy ending for all involved.