How can I get a guy to like me enough to stop talking to other guys?

So, as it always starts: There's this guy who I like, and he likes me too,He's funny, intelligent, and an all around nice person. We talk almost everyday, and when we do it's for hours on end. I've gotten hurt in the past, and been with the wrong ones, but I honestly feel that he is the right one. There is only one problem. We have decided to be completely honest with eachother, and he told me that he is talking to another guy besides me. I told him that I was OK with that because we aren't a monogamous couple.But we have really great Chemistry, so is there anything I could possibly do or say to give me an advantage over the "other" guy"? Again I really like him, and feel that he may be the one.