Why does he do this

My freinds boyfreind is soo mean to her but liek he loves her so much and she lieks him a lot to but he treats her like sh*t and like tells her she’s not trying hard enough to be with him and shes trying wwwaaayyy more then him and I jsut dont know what to tell her I’ve been trying to help her out wiht this and I yelled at him for her when he told her he didnt care and told her to shut up. I cant belive she still with him I jsut dont know what to do