The only problem I see is the sentence "You are the only girl I'd ever go for..."
I took that as something akin to "you're my one and only." Not so much about "I'm straight but for you (although that happens sometimes) but more about "I don't want to be with any other girls".
Which makes it another case of "If it's you, it's okay". So, you know... she's not gay. If Fujimaki gave her the okay, she'd drop the lesbian relationship.
That's not really fair. She has feelings for Fujimaki, but she also has feelings (serious ones!) for Yukimori.
It's a pretty underhanded way to water the gay down.
As someone that is bi, I kinda gotta say, bite me?
They didn't "water the gay down". She's bi. Or straight with an exception. That's valid and doesn't undermine their relationship or the fact that they ended up together.
It really irritates me when somebody acts like being interested in the opposite sex somehow demeans or invalidates same-sex romantic relationships. I've been in love with girls, I've been in love with guys. All of those relationships were important and meaningful to me.