Some life lessons are harder to learn than others. You can't "get your man back" like he's some sort of possession. I don't know all the details of what went on, but he's made his decision and moved on. You need to absorb the life lessons you've learned from the relationship and move on, too. If you do, you will know how to behave properly in your next relationship.

I am sorry you're hurting. Keep breathing, take a break from dating until you've healed, don't obsess on him, and move on with your life.