Most Helpful Guy
He's got issues or he's insecure. Why he'd go back to someone who cheated on him AND isn't that mature is beyond me. And choosing a girl over someone who's been there for you longer is a big mistake (this goes the other way too - girls choosing a guy over their BFF).
You need to find someone else because this fella needs to focus on himself. He needs to mature and learn from his mistakes. Maybe once he's done this, you two can have a happy and faithful relationship.