Are you my boyfriend?

I'm dating someone and we're really serious about each other but he hasn't asked me to be his girlfriend. he tried to before and I asked him if he was sure. he said nevermind. i asked him again recently if hes my boyfriend and he said "im more than that" im kind of unsure if we're on the same page. advice? I just want to be sure we're exclusive and I want him to know that from now on if hes doing anything with other girls its cheating.