Is this considered cheating? (..please?)?

I have a boyfriend (Clayton), which we really like each other. I have an ex (Ethan), and we're in love with each other, he has a girlfriend too. I've been telling Ethan I love him (not in a friendly way) and he's asked me out and I said no because Clayton. I REALLY want to go out with Ethan, but I can't dump one guy for another. Thats cruel. I also still like Clayton though and I don't want to crush him or people to think I'm a slut. Advice? Am I cheating? Am I a slut for doing this?