Just explain it the way you're explaining it here. I'm sure if she loves you, she'll understand.

I've been like your girlfriend in a situation before lol. I was dating a guy, and would be sexually playful in public places, like the gym. I would pat him on the ***, or say things like "I'm gonna squat like this on you later." I thought I was being fun and sexy but he said he likes gestures like that to be private. I understood but unfortunately it was just one of the many clues that we just weren't compatible. You girls sound like you're in a much better situation than us though, so see what you can do to make it better.