What are the red flags to a fuck boy? Or someone that just wants to have sex with you?

Im very paranoid about that.. like when I meet a guy I always think that is his intention even though he is really nice and we talk and doentseem to want to have sex with me I mean only wants ..

I just always assume that's what their looking for! Like I said even guys who just hang out casually with me we talk laugh talk again do stuff together and it really is an issue for me I never know and I'm never really comfortable with any guy