One of the most worst things that you could ever do to someone. If you're not happy with who you're with, then fucking leave them. There isn't a use to staying around when you don't even feel the same way anymore. Don't think about how much you're going to hurt them, of course it's going to hurt them. But cheating on them would be worse than just breaking up with them. By breaking up with them, you're giving them time, time to get over you. By staying around just because you don't want to cause them pain will just give them false hope. Causing them even more pain. As each day goes by, you're only making them suffer more and more as they fall for you even harder as each day goes by. If you're not happy, then leave. It's as simple as that. There is no excuse for cheating on someone. If you did it, then you did it. The end. So do the one that couldn't handle losing you a favour, leave. While they're still capable of going on without you. Don't leave it too late. You never know what could happen to them if you've been there for them too long. They start to lean on you, you become apart of them. They make you their everything and once you leave, they'll be left with nothing. So leave, while they still have something..