Hello, I'm 20, there is this beautiful girl i have been in love since i was 18 and during this time we have not really gotten intimate apart from cuddling and kissing occasionally. Last 2 months we decided to try having sex, but i noticed my penis wouldn't just respond to every touch from her. However every other time when we would just cuddle and kiss, I will be as hard as a rock. As we were try to have sex, the thought of her sisters in the other room keeps flashing into my head, I don't understand if this could be the cause or am i having erectile disfunction? i just get nervous and i can feel no life on my penis. What should I do?