You said that he left you because you were “slipping away” from each other. What changed in the two years that you were together to cause him to lose interest? What have you done differently and how do you behave now in comparison to how you behaved when you first caught him?
Two years is a significant time to be together, so there has to have been changes that caused him to leave. These are what you need to look at in order to get him back.
Let me know if that helps, and how things go. I know you’re in pain, but don’t react and act hastily. Be thoughtful.