Why does the person that likes me start mean to me when I finally told him i like him back after 2 years?

This guy has liked me for 3 years. We have been friends for that long, he has pursued me and I have let him know last year I like him too, he got angry that I told him that and we stayed as friends. As friends he is so nice to me. Just recently I let him know again I had feelings for him again, and he has started being hateful and eyeing other girls. What is going on? It is obvious to everyone that he is infactuated with me.