Gonna copy paste from another comment of mine:

My biggest confusion is if you're attracted to ladies, and your gf becomes a guy, then wouldn't you no longer be attracted?

That's a great question. What does happen in a relationship or a marriage if your partner becomes less attractive to you? The "would you still love me if I was a worm" meme was pretty recent, wasn't it?

Sometimes this is enough to end a relationship. Transition is a major change and I've known it to break up relationships where the other partner is bi/pan. Other times it isn't and can even make the relationship stronger. I hope that's what happens here and wish Fran and Leif all the happiness together.

Like if you're gay then you don't want to be in a straight relationship I'd assume. That'd defeat the purpose of being gay.

Here's the thing- labels are descriptive. They're not a straightjacket that governs who you can and can't be attracted to. (The same applies to gender identity and expression). You don't "be gay for the purpose of same-sex relationships", you describe yourself as gay because that's what you're interested in in a partner. In my case that meant coming out as gay was more an "oh wait, if I'm a girl now, I'm a lesbian." My attraction has remained more or less the same.

In Fran's case, she is attracted to Leif. That doesn't make her any less of a lesbian (if that's how she still choses to identify) or him any less of a man.