You've outlined the biggest problem with overlapping friendship circles. Everyone feels they have stake in each other's business and relationships. When one relationship goes sour, the ripple effect strikes everyone in the group and people may feel the need to take sides. In breakups/divorces, one side usually gets to keep the friends, and someone else is cast outside the circle. That's usually dictated by who is considered the bad guy, and who is considered the victim. You may have to be willing to blow up the circle. If your boy's girl feels uncomfortable with fucking the friend of the guy that rejected her girl, she'll have to figure that out for herself. Don't keep fucking/hanging with someone you'd rather not be with because you're afraid of collateral damage. Let it sort itself out.
"The best kind of pride is that which compels a man to do his best when no one is watching."