How to keep a relationship from being purely physical?

yes . TALK to him. I completely agree with Euro raver. Make sure that you make it clear to him. Tell him you don't want this to become a physical relationship. and you'd rather have your friends around him too. And that he needs to understand that.

you should invite him to places that you go with your friends and let him know that itll be fine to hang out. cos the more you hang out . the more he'll get what he wants too. (its like motivating him . especially if you want to be with him that much)

Try to meetup at places other than your house or his house and try to get more conversations going. One thing usually leads to another and you pass the time.

If not maybe get a group of your friends together for a movie night. That way you guys can sort of cuddle but nothing too sexual in front of your friends.

If anything else, TALK TO HIM about it. A lot of the time us guys have no idea what a girl is thinking until it's too late.