Please help, is there any solution to fix this other than breaking up?

I would say stay with him if you are comfortable with being his second choice. If he was 100% for you, there would be no "I like you, but I really want to fool around with this girl, but I don't want you to hold it over my head". Because that's whats happening. There are other guys out there for you, and he is doing nothing but holding you back. Especially now that you are getting older and are able to start appreciating things and people in a whole new way. He's not confused. Whenever you tell him that you will continue to see him after he is done with the other girl, you are only feeding his ego. And its working. Good Luck :)