I've had about ten girlfriends as well, but I never had sex with half of them. I suppose it was because we wanted to be serious about each other, so we were a little more reserved.
我交過的女朋友也差不多有十個，但有一半沒上過床，我想可能是因為彼此覺得要認真交往，所以反而比較矜持。