Lost all hope?

Six year relationship just ended less than a month ago. He broke it off saying hes been doing coke behind my back the last year and couldnt continue lying to me so he wanted time to get clean and better himself for us. Were 22 and have been together since we were 16, hes my first boyfriend. I know I deserve better and can do better, hes done me wrong many times and Ive never done anything to threaten our relationship, he was a mean/selfish boyfriend. These last few weeks weve been texting and he said were fixing us and working on us and that flirting/ seeing other is considered cheating. Today I saw that hes in a relationship and has been seeing her while he was away at work (job I got him)and apparently while we were dating. I feel crushed and cant stop wondering why I wasnt good enough or how could he be talking about started a family together with me one day, saying hes in love with me still and be with someone new the next? Idk this is hard, I feel done with life and everything else.