How do I get over this 5 year relationship/first love?

I have been with this person since I was a few weeks shy of 16. I am now 20, almost 21. We have done pretty much everything together. A lot of firsts together... I think that's why this is so hard if you get what I mean. Anyways for the first few years it was good. Then he cheated on me but I forgave him. About 2 years later he left me for this woman he worked with. I, like an idiot, waited on him until he was done with her. I was about 18 at the time. Sooo wrong I know, but I loved him. Now at 21, he said he is tired of doing the same old things over and over. Of course I don't want him to go but I know that this is a cycle that I need to break for my best interest. I hate all the heartache. I went for 3 days of not talking/texting him until he passed me on the road and he texted me saying he missed me. Later that day he said it was a mistake that he even texted me and now, 2 days later, I still feel the strong urge to text him. Please someone tell me how to stop this. I hate this, I feel like there is no one out there for me and if there were, I'll probably just end up comparing them to him. Any advice at all would be helpful. Thanks a lot :)