I think this is a personal choice either A: give a shit weather she has a boyfriend or B: don't give a shit. wat we say aint gonna make a blind bit of difference. I wouldn't kill a snail on the side of the road on purpose but if some one gave me ten pounds I would do it it's called being a cunt if it gets you wat you want. some peeps are like that others not. sleeping with someone elses womon is obviously wrong so either accept being a bit of a cunt or be a good boy. choice is yours in the end none of it means shit cos we all gonna end up dead.
in front of him is really stupid cos you're just gonna get your head kicked in and even if you win i doubt she'd give her number to you after you just beat up her boyfriend.