Leaves ya right after his done f***in ya, only calls you when he wants some booty, never does anything w/ ya in public or w/ his friends. never takes you home to meet moms or dads. never says to ya "where do you think this is going"...those are all reasons for a f*** buddy.
A better question, is what are the signs he doesn't want sex? Except for guys in the most dismal of relationships, they most always want sex whenever they can perform. Early in a relationship, all we want is sex. Once we get to know you our sexual appetite may dissipate as we look for something more emotional.
Women are nearly our opposite, they want an emotional relationship first and then the sex gets better from that. This is what keep sit all going in my mind.
First it depends on personality. Guys who visualize you as someone to enjoy sexual pleasures with will spend less interest or no interest at all in your personal life, activities, friends, hobbies, etc. Sometimes 'friendly' guys seem to want more than that while everything is hidden behind their behavior. Most important thing is to stay tricky yourself and not to give up easily on however man tries to gain some 'ass'.