Most Helpful Guy
Because he hasn't moved on. So he doesn't accept you have.
Most Helpful Girl
There could be a variety of reasons why he could be mad and upset but I honestly would say it's because he isn't the one to move on first , since he's the one that dumped you he would think all feelings for you are gone but if he is putting you down he's trying to take out the regret he may feel for dumping you and bring you down almost so he has a reason to be upset. If your really curious ask him !