I like my friend girlfriend? Hmmmm?

Okay, RED FLAG right there. In every relationship whether romantic, friendly, or with family, there are boundaries. And your friend's girlfriend is way out of the question. I understand that you can't control your feelings, but that's a line you can not cross without consequences. Think about it, is it really love? I doubt that it's anything more than an infattuation. If she's worth completely ruining your relationship with this friend then go for it. But otherwise......