Why do I have so much hate for my BF?

I love him. I see a future with him. We were so happy a few months ago but now all we do is hold each other while one of us breaks down. He has feelings for someone else which are pathetic by all means bc she does not love him. (they never went out)I think its unfair bc I do love him, but I feel unappreciated and betrayed bc I have to comfort him while he struggles to keep himself from leaving me. He says he wants to stay with me bc he loves me as well and he is seeking professional help. My self respect and self esteem are screaming at me to ditch him and make him pay for all this unnecessary stress thats had a toll on me financially and academically. I have so much anger built up inside . Its like I want to punish/curse him out to the point of tears for what hes done but at the same time I can't but I know I genuinely love him since I care about his safety and well being. I want to be able to love him like before without this vast anger tainting it. What should I do?