HELP???? 10 PTS BEST ANSWER???Why is he acting like this?

My ex was mad at me for something so he dumped me. Then he started seeing someone else. For a while it was awkward between us. But then I said hi to him and he acted nice too so it seemed things were less awkward between us. But then the next day he seemed to avoid eye contact and almost give me resentful looks. He does this most of the time, but other days he stares hard at me and tries to get my attention. Makes no sense.