Most Helpful Guy
Break up with him. You don't love him, if you do you wouldn't have those thoughts. There's a problem, you either try talking to him, or you break up. Cheating will just make you a scum, and he most likely will tell others what happened, and you'll gain a reputation.
Talk to him, if things don't change, break up.
Most Helpful Girl
I think you should both sit down and talk about the relationship. You both seem to be unhappy in it and it's leading you to think about cheating. Talk to him and figure something out. Cheating is the never the answer. If you're unhappy, then just leave.