My friend keeps adding my other friends on Facebook?

[-Alligator Sky-]

One of my close friends constantly adds people in my friends list. I don't get it, and I've asked him why he does it and he says Facebook is for "Adding everyone and making new friends." Every time I become friends with someone on there, it comes up on my timeline that he's become friends with them too. He adds people that I've been tagged in photos with or who write on my wall or even who comment on my status. I have several friends who live overseas and he even adds them. They message me asking me who he is and telling me he's asking them questions about me. It's so creepy! Is there a way that I can block him from seeing my friends list?