how do I deal with this breakup

my ex and I dated for 6 months, but I fell in love with him the second I laid eyes on him. I'd stay at his house for weeks at a time, and I was cheated on regularly, but was constantly told I was being paranoid and crazy or jealous of "friends" when I'd ask him about the shady shit he was doing. When I finally called him out on it straight forward because I finally had solid proof, he dumped me and kicked me out of his house. this happened about a month ago, and I've just been driving myself crazy trying to figure out what's wrong with me. since then he told me he'd slept with someone, and I didn't ask who. he later told me she was 45. he's 25. I'm 20... like he clearly has issues but I'm still finding myself thinking about him every day and like trying to talk to him even though I know I shouldn't. how do I cope with shit like this?