BF Made A Joke. Now I'm Not Sure If I'm Straight.

It all started when my bf (m28) and I (f22) were lying in bed together, discussing fantasies. My roommate, J (f22) was asleep in the other room.
BF: "We should have a threesome"
Me: "Maybe? What kind are we talking about here?"
BF: "You, me, and another girl"
Me: "Hmm, I don't know. Can I pick the other girl?"
BF: "Sure. I mean, I know who you're gonna pick"
Me: "Do you? Who?"
BF: "J"
Me: "What? Why would I pick J?"
BF: "Come on, you're both clearly into each other. And I think she'd be alright going with me if we play it cool"
Me: "Well, we're both straight, so it's not gonna happen"
BF: "Sure. Whatever you say..."

I haven't been able to get J out of my head ever since that conversation. We are really close friends, but we're both straight. But I can't deny that we've walked around naked in front of each other casually. We have showered together platonically a few times before. We did once kiss when we were drunk.

Now I can't get her out of my head. Looking at her body makes me wet. I've never had feelings like this for another girl before, but now I desperately want us to fuck.

I kinda just want to grab her and kiss her while fondling her body just to see what happens...