Why do people cheat? Why dont they just break up with their spouse if theyre just gonna cheat

It's not so cut and dry. Just as no one has the same personality as another, the reasons for cheating are just as varied. Some people will cheat because divorce is too expensive. Others cheat because they enjoy the thrill of doing something they shouldn't be doing. Others because they love their spouse but sex is too routine and they need something to shake it up. When someone says "we're only human" it's because we are prone to making mistakes. At the end of the day, I think cheating simply stems from selfishness.