Dating a Trans woman, explaining to friends

I'm an openly gay man and am dating a trans woman. I fell for her before she came out as trans and we had broken up before she came out as trans as well (reasons unimportant to topic). We recently started dating again and a couple of my heterosexual friends are having trouble understanding why I would date a woman. They've asked if I'm suddenly straight now, if I'm bi, or if this is a phase for me. I've tried to explain as best I can, but they're still confused. I've ended the conversations with "I love her, why does it matter what my sexuality is?", but I know this will be a repeated conversation in the gay community as well as with my immediate family, so I'm looking for advice to explain it better.For the record her being trans does not, nor has it ever effected my feelings for her in a negative manner. I'm only looking for advice to explain this to confused friends.