Ex boyfriend problems --- help please!?

okay so my ex and i were together for like two years but we broke up about 6 months ago and he has been dating someone else for the past 4ish months. after we broke up we of course still wanted to be friends however that hasn't been the easiest thing. After a guy friend and i were having a convo on my fb, he chated me saying that i shouldnt flirt on fb because it sends out a wrong message, and when i told him it was none of his buisness he gets all defensive and says that i treat him different then other friends and that he is only looking out for me. after a little fighitng we started over again but then one day when we were planning to hang out, he asked me if i had hooked up with anyone since we broke up, (mind you he has a gf) and i told him yes, then he asked how many and i said four ( all of whom i have known for a while and it was over the course of five months), then he proceded to tell me how im being self destructive and essentially slutty and i should save myself for someone who will fall in love with me with one look at my smile...again i told him my relationships with other guys is none of his business and again he got defense and said i am treating him different ...after more fighting we starrted over AGAIn. we chated maybe once every 2 weeks for five minutes jsut to check up on eachothers families and stuff, nothing flirty at all, when randomly about a week ago i got a three paragraph email at 1 in the morning saying how i need to be strong and get over him ...when i told him i was over him i have no idea what hes talking about, he refused to believe me and he was like you always said you would be honest with me, so tell me do you want me back? ...of course i said no, then i looked on fb and he untagged all 100 photos we had togther...i jsut don't understand him..anyone help? He has a girlfriend and he broke up with me, so i don't know why he keeps doign this.