How can I get him out of my head for good?

It's good that you got yourself out of that situation. I would surround myself with the exact opposite kind of people. People who you'd want to emulate and look up to. We are who we surround ourselves with. Also keep busy. Hopefully whatever job or position you're looking at will keep you busy and besides that, make some time to have fun- go mini golfing, hang out with friends (I don't know you so those are the best examples I can give). Do what he won't do- live life to the fullest. Hope this helps.