Ex boyfriend drama, and heartache from a betrial of a friend...?

Me and my boyfriend went out for a year. At first everything was rosy and nice. However toward the end of our relationship he became really controlling, jealous and emotionally abusive. He would start a fight over NOTHING and Everything. One day I could not take it anymore and I broke up with him, and left for a month trip to another city (i had to get away from his dramas). When I came back he tried talking to me, but it was all part of a play with my mind again, and after all, i really did not in any case wanted to put my self back in the situation I was in before. The other day, my friend calls me and tells me that she saw him, getting some space with another friend of mine at a party. She said she had seen them together talking for a long while. I know the girl he was talking to, and i had trusted her as a friend, but thinking that something is going on between them is really bothering me. Mostly because I feel like she is betraying me, rather than him. Any suggestion 2 feel bette