Whats wrong with him!!!!????(GUY)?

So long story short. So i have an ex bf named sam me and him dated all the way from freshman year to junior year summer I am now a senior. He cheated on me. So any way I was at a party and he was there to (first of all let me start by saying I am a teenager and i do dance on guys who cares its a party) this really really hott guy was sitting down and he pulled me over to him to dance i was grinding on his lap dancing and then i turned around faceing him dancing. we were dancing fo about 20 min and then out of no where sam comes over tripping out calling me a whore and slut and skank and talking about how he hates me and never wnts to talk to me again. I honestly dont know whats wrong with him we have been brokkenn up for MONTHS! whats his deal?