Why does he get pleasure from hurting me?

Why does my boyfriend constantly put me down.... hes nice to his friends who do nothing for him .... whereby i do everything for him i always bought him nice things for christmas and birthdays and he knows i dont have much money but he doesnt mind taking the presents and demanding more... hes nice to start with when he has the presents but then i get treated bad again.. he tells me to go away alot but then if another guy hugs me to cheer me up he hates it and gets so jealous .... he wears the stuff i buy him but doesnt mind sneering at me when he wears it and not wanting to be around me.... but he always wants to be around guys who are never there for him when he needs someone but hes all smiles with them... hes always horrible to me ... and he knows he is cause he grins when he does so .... so why does he get pleasure from hurting me? after everything ive done for him can some people actually be this horrible?