STUCK:(

So today I got a message on Instagram from a girl with pictures of her and my boyfriend talking. He was basically calling her pretty and lying about our relationship because he was apparently “horny”. I called him hysterical crying talking about it and him calling me a bunch of times and he was hysterical crying and saying how much he loves me and can’t lose me and everything. He says he is horny all the time and says he would get help. We live together at my parents and he gives them money every week but I love him a lot and don’t wanna lose him but I don’t know how I would be able to trust him. Any advice would be appreciated.