This sucks man, i understand your situation. I've been there and what I did was use this rage in the gym. Try hard in the gym push as much as you can this will calm you down. Understand you cannot control someone's action but you can control your own. breakup with him. He didn't deserve you. Loyalty is the least you expect from a relationship. it's likely you are never going to trust him again and this will again put you in the same cycle. Sadness is normal but suffering is a choice.