Most Helpful Guy
by his behavior if he move things between his girl and him fast you'll know that he just wants sex, or the guy flirts with you and say i dont wanna hurt you crap at the same time, its also a sign of that he just wants sex, or he will say something that will lead the relationship to friends with benefits.
Most Helpful Girl
If he is interested in getting to know you, it should be pretty apparent. He'll ask questions to learn more about you and be willing to spend the time to hold conversations with you. Make sure to show him the same behavior if the interest is mutual. If he is only interested in sex he might be a bit speedy when making out, quick to go under your shirt or take your hand and put it on his crotch. Now of course he could still be a nice guy and just be excited, so make it clear to him that you want to pursue something deeper by telling him exactly how far you'd like to go that night. Make sure not to waiver, the foundation to a good relationship takes patience