Just read this so I'm sorry about the lateness but you've done fuck all wrong and if it feels like you're brokenhearted then do things to take your mind off her.
When I split up with my first love (not saying that she's yours, I'm just trying to relate), I sank into a deep depression and didn't know what to do but I went out and met new people (friends, not girls) but it turned out that the girl that I met and saw as a friend is now my girlfriend and we are madly in love. The thing I'm trying to get across is that life in unpredictable so if you leave her and her weak self to it then you might be as lucky as I was and catch a break.
Also, like unsworthblue said if you play it cool and make yourself scarce from her life then she will start to think 'Hold on, why hasn't he text me, or called me, or tried contacting me? Maybe he doesn't miss me', then, as a girl, she will get paranoid and will want answers from you which will lead to her calling you and everything will leak out then.
As for the guy, fuck him (not literally), he sounds like a right clingy, over-protective, weak male.
Good luck with it all though mate, I hope you're starting to feel better since you started this a few weeks ago. And I hope that you turn out to be happy and make the right decisions.