Why is it so hard to get over this jerk?

I'm 17 & have been on & off w/my bf (20) for 4 yrs. He used to be nice but all he's done since finishing high school is sit on his *** playing online videogames & flirt with a bunch of tramps. Basically he's become a jerk. He calls maybe once every 2-3 weeks and will randomly stop our conversation. He tells me he "loves" me all the time, but his actions say that's a bunch of bs. I've dated other guys,but he was my first bf & the only guy i've ever loved. I just wanna stop being in so much pain! That's all i feel with him anymore. He doesn't have a job & doesn't plan on college. So....why can't i get over him??? I'm just going to leave him & not even bother telling him it's over. He can't even get so many girls in real life so what's with all the online tramps?? He's even told them he "loves" them! Wtf! He makes me feel so bad about myself, so why is it so hard to let go?? I hate that he's changed so much. It's like he's only there for me when it's covenient for HIM. He told me to go on msn a few days ago so we could chat, so I did. After maybe 15 mins of talking, he said "damn gotta restart my pc. brb". So I waited....and waited. I was using my phone so I went on to check if he was back every now & then. He never came back and I know he went on facebook later. He'll also text me, i'll respond, and he won't say anything back. Why start a conversation with me if he won't continue it?? I never see him since he's been at his sister's house since december. He said he'll be back in a few weeks. That was a month ago. He says he wants to spend time with me on July 4th. Why such a long time from now, and why should I make plans for him anyway after the way he's been treating me?? Why can't I get over him if all he does is treat me like trash??