Most Helpful Guy
I know you know the answer here because the first line of your post is about the only thing that makes sense. Yes, you need to get over it but more importantly, you need to forget about him and think about yourself. If you want to get with other guys or even have casual sex with a new guy every night, it's just fine -- but do it for yourself, not for him. I mean, of course you felt horrible the next day because you nailed a random guy hoping it would make some other guy jealous. Everyone involved in that transaction had a great time -- except you.
I understand that you're hurt, sad, and you feel discarded but don't worry about who he dates or what he thinks. I can tell you that he probably doesn't miss you and he has spent about as much time thinking about you in total as you spent writing about him above. Find a guy who's worth your time and actually more importantly, spend some time respecting yourself rather than making everything about a guy.