The best way to figure out whether your girl likes what you are doing to her is to see if she is moaning. You don't gotta be Sherlock Holmes to figure out this kind of thing, though. I mean, if she likes it, she'll do it loudly, or she'll breathe heavily, or she just might let out a scream of pleasure sometimes. But primarily what you're going to be hearing while you're fucking your girl is going to be moaning, if you're doing it properly. Some girls tend to be kinda quiet, sure, but there is bigger pleasure other than doing it to her so well that she can't help it but let out some moans whether she likes it or not. If you don't got a girl to do this kind of thing with, though, you can just check out porn in this category. Don't deny yourself this pleasure.