Sex before relationship

Do you think a guy respects you less if you have sex before actual commitment? Will he ever be serious about you if he has sex with you before making you his girlfriend? I was recently with a guy that gave all this talk about him wanting me to be his and seeing us together in the future but now I feel like it was all a lie and he was using me. He ended things to get with his ex but I know he had to have some sort of feelings for me. I'm so confused.