Is it normal for you and your friend to exchange sexual touching?

My friends and I exchange touch. In other words when my friends are over I will lay my hand on there crotch and they will lay there's on mine sometimes. They never say anything about it so I keep doing it. Sometimes I even go inside there pants. I'm a 19 year old boy. This happens with girls and boys.
Is this normal or should I ask them if I should stop. This is not a fake question.