How do you know when a guy is just using you?

fwb (friends with benefits), most likely, if you don't like it, then stop doing it, simple as that

he is definately just lonely in that department. you can't expect him to go out with you because ur already giving him wut he needs. never have a sex with a guy you want to be in a relationship with unless you are going out with him because if you give all of yourself away when ur not going out, then he has no reason to be going out with u. he is getting everything he needs, and since he's not ur boyfriend he has every right to be going out and doing the same thing with other girls. he is most likely using u.