Pretend you're on the outside looking in: would you want to be friends with someone who can do this to someone he supposedly loves? I sure wouldn't. If he'll screw over someone he "loves," then he'll screw over a friend in a heartbeat.
Your emotional, mental well being is not worth the abuse this guy is putting you through. Not much to lose, really.
But the thing is... He's one of my best friends, and I'm afraid that if we completely call it quits then I'll lose him as a friend.... I know he's not good for me in a relationship but he's one of the bestest friends I have ever had.
Move on. This guy has cheated on you before and now broke up with you */for ANOTHER girl/.* And he obviously feels like he has nothing to worry about because he thinks you'll still be available in a year. He does not value you as a person. He sees you as a convenience, a fail safe to run back to if something else he deems better doesn't work out. This man has shown you at least twice now that you mean NOTHING to him.
Move on. You can do so much better. God says to forgive, but forgiving does not mean you have to get back together with someone who has mistreated you this badly and disrespected you this badly. You're not married to him, thankfully. I would truly take this as a sign it's not meant to be and move on.