Questioning Gender Identity

My best friend who I've been on again off again dating and fwb with (it's complicated) recently told me he's been questioning his gender since as early as Jr. High. I'm totally supportive of him and I just want him to be happy. But I'm worried that it will change our relationship. I'm somewhat bi, I'm sexually attracted to both but have never had a romantic attraction to a women. I'm worried that it will change things. Has anyone here been in love with a man and maintained that love through their transition to a woman? I know it's not about me and no matter what he has my support its just complicated trying to be a good best friend but also being in love with him. Any help is appreciated.