Most Helpful Guy
Friends with benefits? Really? Can't you guys keep it in your pants? If you're friends with benefits then you have a VERY small chance of dating because you just have sex when you feel like it. Guys use those kinds of girls.
Most Helpful Girl
It will NOT advance into anything else. The second you became friends with benefits you secured that you will NEVER be his girlfriend. Emotionally, you are now in a completely different box to a potential girlfriend, he would need respect to have you as a girlfriend and if a guy is happy just fucking you when he doesn't like you, he definetly doesn't respect you.
I've done friends with benefits twice and both times I had feelings for them and both times I got insanely hurt/heartbroken. Please heed my warning, it's a terrible idea. Tell him you have feelings for him, and it's either a relationship or nothing because your feelings WILL NOT go away and eventually his lack of feelings and interest in other girls will become very evident, and trust me... Seeing them hit on/get with other girls while they're fucking you is the most painful thing. And they WILL do it because you're just keeping their cock wet while they're looking for the right girl. Please get out of this arrangement if you have feelings.
Good luck and always be strong :)