- Can't stay friends
- Can stay friends, message her apologising
- Can stay friends, but leave her to talk first
Most Helpful Girl
Most Helpful Guy
It sucks, but you gotta back away (no contact, unless she initiates).
First, it's the right thing to do. She has history with the boyfriend and you're meddling because you like her. If she broke up completely, then the story would be different but you're not a "friend." You're a guy she like romantically (and vice versa).
Just think, if you were trying to work things out with an ex, would you want some other dude sniffing around - pretending to be her "friend" when he really wants her as a gf? No.
Second, backing away will make her miss you more (depending on how much she likes you). If things don't work out with the boyfriend, you'll probably be the first guy she calls.
Last, don't apologize. Don't explain. Speaking from several experiences like this, you'll either never see her again or she'll have a fight with the boyfriend, dump him, and coming running to you. Either way, don't sit around waiting. Meet other girls and don't sit around all miserable hoping she'll call.