How should I deal with 2 friends?

I have two friends from marching band and they started dating about five months ago. They are about two years apart in age, she is older. I found out this week from his best friend that he has been flirting with other girls to the point where it would be considered cheating. My problem is, I don't know how to confront either one without losing at least one friendship. I don't want her to find out the hard way, and I don't want the guy to get caught the hard way. How should I confront either one of them about it?How should I deal with 2 friends?
I would go to the boy first and ';question'; him about it. don't accuse, just question. let him know that (if its happening) that if it continues and he isn't honest with her, you'd have to tell her.How should I deal with 2 friends?
that dude's cool
don't do either.if you have to ask on yahoo youre already a crappy friend.it shouldnt be that hard of a choice