Some people have a thing about their partners getting involved with friends and family. There's nothing wrong with that--if you are clear about it up front, and if you state it as a boundary ("I can't be involved with someone who's dating one of my friends or family members") rather than a rule ("You can't get involved with any of my friends or family.") Was your guy aware before he met your friend that you have a preference against your dating partners getting involved with friends of yours?
While you aren't wrong to have that preference, if you told your guy that he couldn't date your friend (making a rule), and especially if you told him to stop seeing her (I'm not clear on whether you did, or whether he made the choice on his own), that was, in my opinion, wrong. You only have a right to manage *your* relationship. Your guy and your friend? That isn't *your* relationship. It's *theirs*. You don't have a right to manage or control *their* relationship. Regardless of how you put it to him, you put your guy in the position of having to choose between two people he likes and wants to be involved with, and forcing someone to choose like that is never okay. He has every reason to be resentful.
Whether he gets involved with your friend or not is *his* decision. If you want to be "the bigger man," you could tell him you've reconsidered and are okay with them getting involved--but make sure you actually *are* okay with it, or you'll be the one ending up feeling resentful. But if you tell him you're okay with it, it's entirely up to him and your friend whether they get involved with each other or not. If you can't handle him being involved with your friend, *you* need to make the choice of whether to stay involved with the guy or not. That is the ONLY choice you're in control of. Not his choices about who to get involved with. That isn't yours to control.
