How to survive heartbreak?

Hi everyone, I recently fell for a guy, in the beginning it was mutual, we had a history, we liked each other two years ago, but then I had a boyfriend, so nothing happened, because I was faithful to my boyfriend at the time. Six months ago, we kissed and after that we tried to date like 4 or 5 times, but I always freaked out, because I liked him too much and he is the kind of guy that doesn't really share a lot of things. We didn't have anything in common, we used to fight a lot, which was really annoying... I honestly don't know why, but I kind of fell in love with him and he did too, we slept together, dated for 6th time and I dumped him, because I got scared that we were fighting a lot and we had nothing in common. I thought it will never work between us in the long term... But I still can't get over him. We are in university together and we see each other a lot, but in a month we graduate, and he will be leaving for the summer. Now that I know that I lost him and I will probably never see him again, I feel so sad and sorry that I didn't believe in us at all... But we both are so stubborn! He pisses me off all the time, he looks at me, talks to me, writes to me, he told me that he still has feelings for me, and I still care about him a lot, but he doesn't want to try with me again, because he is scared that I'm gonna hurt him again, and that we both bring the worst in each other. How am I supposed to get over him, to stop missing him, so that I can focus on my exams and stop feeling so sad and stupid?!?!