A childhood belief about virginity

I heard the word Virgin from my mom she told me it was a girl who had never slept with a boy, my cousin was a boy and we slept in the same bed all the time so I thought I wasn't a Virgin any more. when we where on the way home from church I told my GRand pa that I wasn't a virgin any more he freaked out and asked me what a virgin was I and I told him that me and my cousin had been sleeping in the same bed and he gave me this long speech explaining what it really ment to be a virgin.