I know my ex still has feelings and.....?

Yeah... I think he's definately using you as a back up. If things don't work out with him and the new guy, then he's got you. That's totally his mindset. He may want to get back with you too but is just waiting for you say it first, or just playing mind games. If you still like him, tell him. But be warned I think he's using you. And if yall do get back together, how do you know if he'll do the same thing he's doing to the other guy now or not? Be careful.