One thing I have learned about relationships is that you need to be direct. Like everyone else stated go to the girl. See what she wants. IF she is interested in you then plan things from there. If that’s the case a good way to get him to back off is embarrass him in front of your girl. Bring it up and make sure every one including your girl knows what you’re talking about. Embarrassing him will work better than throwing punches. Although I do suggest punches if he doesn't back off. Some guys

just don't get the idea of "my girls taken" and think any girl is free game. Good luck with your first one. They are always a handfull.