How come I still think about my ex who treated me crappy?

I am 22 from NYC I just got out of something really bad with an ex and I can't believe I even thought he was a good guy even though he was very nice at first he turned into a very mean and inconsiderate person, I don't know how u can be nice one minute and then be vicious the next. Anyways with that said, its weird because I can't get over him, he is someone I can't shake and I've never been like this before, I check his facebook, including his new gf whom he never told me about cause he was dating us at the same time to see if he's as miserable and sad as me but then I get sad and angry all over again, what can I do to get over this? I'm a scorpio so we dwell over things for a very long time and I keep asking myself, what did I do wrong, did he care about me or is he still thinking about me, he's an aries so I know he probably forgot all about me, I just want to know how I can forget and move on, I won't give other guys a chance and idk why. Its been two months since I spoke to him in which he called me pathetic and told me to hop off his dick because I exposed him as a cheater to his new gf, please all advice appreciated. What do i do? How do I stop torturing myself by wanting to look at his facebook? How do I stop feeling so down?