If a girl really likes you, will she withhold sex as a way of seeing if your really interested in being with her or if you just want to have sex with her?

Maybe... or maybe she is just withholding it because she isn't ready for it yet... ever consider that?

She may want to be a virgin on her wedding night.

There are a million reasons you won't get sex from a girl. She can like/love you but not want your baby.