lost&confused

I have been involved with the same guy since I was 15 years old (I'm now 21). We've always been very off and on and even dated other people. Well we both ended up at the same University out of state (3yrs ago). Since then we were still on and off but mostly on! We always break up but this time is different. About 3 months ago we stopped talking again and I wasn't there for him while he pledged a greek faternity. About 2 weeks ago I started contacting him again, but he was very distant even ignoring me but we've had sex within this time. He is always usually distant at first when we stop talking, so I didn't pay it any attention. As of yesterday we went to lunch and he dropped the bomb that I wasn't there for him when he needed me the most and that I didn't try to be there. Also he told me he was no longer in love with me. Now for the past 6 years I've always been there for him when he needed me, and because I wasn't there this one time he's done with me!!! Also he's talking to another girl and he said the only reason I care about him now is because he's talking to her, but I swear it isn't! He said she was there for him while he was pledging and I wasn't! What do I do!?

I keep trying to convince him he's just mad & I know thats pushing him away further, but I'm not ready to lose him. He won't respond to my messages, should I leave him alone?! I've never doubted his love, but this time I really think he's gone! Or is he?! What to do?!