Umm.... I've had a dream of "messing around" with my best friend. Woke up feeling gross. Ugh. He was like a brother to me. It doesn't mean you like him. Dreams can mean something but not always. And not to mention you can't control them.
I would say it depends on how you felt when you woke up. If you woke up feeling guilty or disgusted it meant nothing, if you woke up with a little curiosity or disappointment it probably means your boyfriend is not the one for you.
I think most on here are wrong (unless you DO have feelings for him). I think the dream reveals your insecurity about your boyfriend's feelings of being not attracted to you or his lack of committment to you (in your eyes). These are the things your subconscious is working on.