I just want some time with my boyfriend?

I'm in a long distance relationship and my boyfriend is visiting for 3 weeks in June from England. We have a very involved "sexual relationship" (lots of sexting and Skype sex and all that) I visited him in December and we just wanted some time alone but his parents wouldn't let us. We are both 18 and are headed to University in September and we aren't being allowed to be alone with each other. Even in June, my parents told me we aren't allowed to be alone together. I feel like that doesn't just put a strain on our sexual relationship, which we want to have but also our relationship as a whole because we are constantly being controlled over our parents. (Worst thing is our parents are really close friends) How can we convince our parents to let us have time? Or how can we get away from them?