Seriously, why can't I stop thinking about him?

My ex. We dated 1.5 years, we've known each other 3 years, it's been over since September, he ended it, got mad, ignored me for 6 weeks! In that time met someone, stopped having feelings for me, but would go back and forth about if he did or didn't have feelings for me and her. Long story short, he chose to be with her instead of working it out with me. He just met her in August! She's a lot younger then us, she's 22, I'm 28, he's 29. We said we'd do the friend thing, he started ignoring my texts and calls again (I didn't over do it, I texted like once a week) but then texted me last week saying she lives at his house now! That hurt so much, we never lived together! I know I need to move on, it's just hard, even at my age. I think about him constantly! Why can't I stop? He hurt me so much with his lies and just everything!!! (Some of his family even questioned why her and not me, they also say she's controlling and tells him what to do) why would he want that over someone who did everything for him, I treated him like a king for almost 2 years! I don't get it! Help me get over this!