What are signs a guy is just using a girl for sex?

If he's not that interested in "you". That means he'll talk lots about his interest but not yours. When a conversation concern you, you'll notice his mind drift to other random things. He rarely asks you about things you have going on and when he does it's only because he's trying to find out when you might be available to have sex. He's not good at remembering much that you've told him about you. He's not quick to include you with him friends or be introducing you to them. But if sexual stuff was the first things you actually shared together, and you see his eyes light up whenever the subject turns to sexual things and he can talk forever about that, you KNOW he's using you.

Watch his eyes to see if it shifts in direction other than your face. That would mean that he is sexually attracted to you. A balled fist usually indicates that he can't take it anymore when he's with you and wants to have sex right away. If he's usually really close to you most of the time or the obvious: if he only talks about love and sex (usually the latter) with you, waiting for a response for his delight.

When everything you guys do or talk about mainly involves sex. If you guys can't just hang out without sex then he's probably just about that.

Basically if he only sees you for.. sex, or if he tries to get it every night, and any time possible. And if he doesn't have normal relationship etc.. And basically what surfshop90 said.

A sure sign is if you tell him that you've felt like you had to in previous relationships to be liked, so he's cautious about trying to keep you from feeling that way, and asks you several times if you're sure you want to.

You might as well say "yes, I'm sure," and then cry later because he forced you into it. What an asshole!

When pretty much every time he sees you, ends up leading to sex...

when that's the only time he sees you or has anything to do for you.

he texts or calls you in the middle of the night but not during the day and usually when he's drunk. he pays no attention to you when he's with other people and you guys are around each other, he doesn't actually ask you out on a date and he doesn't ever want to know you as a person excluding all emotions from the picture.

Id have to agree with all the answers the guys gave xD I couldn't have said anything better myself TBH