Why does my ex-boyfriend hate me so much?

He must have thought that there is something going on between that guy on couch and you. It really hurts alot to see dearer one with another. In my case also, i dont used to like my gf being out with others. I dont know why, if there goes something or not but I just dont want to see my gf with others. I get freaking jealous and I dont know... If I were in ur Bf's place i were to smash that guys face... give such a blow he will never forget...