Dear Bitter Amanda,
Let's say there was a guy and a girl that broke up, and I got to know the girl after. Now, let's say we started seeing each other, but then the guy comes back and wants the girl back. Say she didn't want anything to do with him, turned him down flat, and is now persistently annoying in his attempt to "win her". Also, let's say things are good between me and the girl, but there's added stress on the developing relationship because of the guy's behavior, and also that the guy annoys me to no end with this crap. What the hell should I do? Do I have permission to beat him up?
Guy sounds like a douchebag. If you break up with and then get rejected by the same girl (or person, really) you just need to move on. There's no sense in trying to be with someone who doesn't want to be with you. Why do that to yourself?
But back to your situation. If things are good between you two, you probably want to keep it that way? You could beat him up--what a typical male response. There are two possibilities. She could think you're her knight in shining armor and that chivalry isn't dead! You could restore her faith in men! Orrrrr...she could think you're a juvenile pig who can't handle things like an adult. You don't think she can deal with him on her own and she needs you to protect her??
See? It's tricky.
If his attempts to win her heart occur while you're together, you can certainly pull him aside and let him know that you're working your magic and he's ruining everything. Doesn't that fall under Guy Code? THEN (and only then), if he still won't leave her alone, you are allowed to consider the alternative. You might feel less like a man, but she'll appreciate not seeing the testosterone circus. And really, that's better for you in the long run. (ie Will improve your shot at getting laid.)
Best of luck, boss.