Why are some men so nasty 10 points for honest answer?

my ex is so nasty about me and i dont know why it is unprovoked. I saw him out he did not speak to me my friends are friends with him, so one of them asked me why he was so nasty. I said sorry i had texted him a bit when we broke up and i did apologise. I said i was seeing someone so there was no need to worry, anyway 2 months ago when he was drunk he had come up to me and chatted to me i told him my cousin had died and he tried to hug me, then an hour later came up and asked me for even though he has a girlfriend! I said NO..and he just bolted - i think he thought i would run in to his arms- i told him the other night how inappropriate this was and how inappropriate could one person be! he said nothing and then started getting really nasty saying dont call dont text - i said iwouldnt i was seeing someone and he looked suprised - he then said he must have been drunk when he asked that? Why oh why is he being such an **** one month he tells me im beautiful n the next is nasty!