Most Helpful Girl
All this over Facebook comments, Christ.
My take is that he was offended you thought he wanted to seriously talk to other girls (when really he just made a few comments on a girl's picture), and that you would bring up separating over it. Both of you overreacted I think. His FB comments likely meant nothing, so it probably didn't need to be brought up, but he didn't need to storm off and not talk to you about it either. I don't think he even wanted to see other people, but he simply got defensive when you assumed he did and suggested breaking up. Just leave it now, it's a big mess, and there's no point analyzing it. He clearly doesn't want to fix anything or talk anymore, so just don't contact him again.
For next time, don't read into what your guy does on Facebook and think he doesn't want to be with you. Sorry to say, but this guy was onto something when he said you were being insecure. You need to trust the guy you're with and your relationship, or it'll fall apart.