Tell him that you really enjoy being with him and that you would like to date him. Ask him out.
In my opinion you need to talk to him and let him know that you would like him to be something more than a friend with benefits. that happened to me and now my friend with benefits is my boyfriend. GOOD LUCK...
Just be honest and open. In relationships, ALWAYS be honest and open. Tell him how you feel. That's it.
Stop being a friend with benefits.
Neila222