How do you know if a guy just want sex?

Lol I'm not sure if anyone is going to answer this general question

I think we're more inclined to help case by case. So if you could give us the facts about your situation.

Easy. Tell him you're saving yourself for your wedding night and then act like that's true. Don't have sex.

You spend your time with him with your clothes on and actively, eagerly trying to get to know him in a charming and sincere way.

If all he's interested in is sex, then he'll move on. That would be a good thing to know, right?

Well I agree with JBeucaire, if the guy is not interested at all in getting to know you better then all he wants from you is sex. When guys start showing interest on who you are as a person and have nice details like send flowers to you, or just send a text asking how you are, go for a coffee or for a walk then you know there is some kind of interest. If you just get booty calls then he clearly just wants sex.

When in doubt, abstain!

I agree with the others.
When I sense that a guy is just looking for sex
I tell them I am not an easy sleezy or sloppy seconds, they are a dime a dozen down the street.