Hey … remember about the … “If you love her, you don’t have to
own her, you just want her to be happy” ? It all comes down to your
gf’s attitude. You can ask her to ask the guy to stop, (and
hopefully he does). Or you can confront him together with your gf.
Confrontation doesn’t mean a fight though ! If he’s serious about
it, then, let him be. I’m sure if you treat your gf well, she’ll
stick around with you and not the new guy. Trust is an essential
thing in a relationship.