What the hell?! LMAO!?

So my ex girlfriend broke up with me this Sunday claiming I was irresponsible and too dependent on her (clingy). She acts EXTREMELY different towards her and I just thought it was the breakup...but the real reason is this guy Doug who she was friends with while we were together and her started "talking" and now they're messin' around (although Idk if they're havin' yet). I know it sounds bad, but I want this girl back because when we were together, she was a great girlfriend, in all honesty. I was kind of overbearing and I'm doing what I can to improve myself and I understand that takes time. But in the meantime she treats me like ****. Now she's supposed to be going to F.I.T. this Sunday to move in and we had arrangements before the break-up and I need to help her because if I back out now she'll have no one to help her move in and that's really ****** up especially b/c she's still giving me $300 for an unrelated reason. By the way, she doesn't know I know about this new guy and I KNOW bringing him up will only distance us more. How should I act on Sunday/what should I do when I help her move in? and then after Sunday, what should my actions be? In serious need of help, b/c I'm going crazy!