Having strong feelings to cheat

I'm a gay man in an a relationship going towards our nineteenth month. Getting a bit slow and arguments are once a day. Nothing big but irritating nonetheless. I have always been that guy who is on the hornier side and feels a compulsion towards intimate feelings a good amount of the time. Lately I have really REALLY been feeling like I want to try out other guys, have some fun, get nasty. I'm only 20 and at this point I'm scared to be committed to only one guy when there are so many out there. It's such a sick animalistic feeling and I love my boyfriend SO MUCH NO LIE but I still feel this way. I have no idea what to do. He constantly says he will leave me if I cheat (as he should, God knows) but he will also not take a break. Not even for a week. I feel trapped in a relationship even though it is just from sex. What can you guys tell me or help me with? Thanks so much.