Tell him to back off..and if it doesnt stop and it gets to the point were your scared tell an adult..it may seem lame but it works. You might not wanna tell his girl because he'll get mad.

I have a solution for that just call him Brother the way her sister calls him,I am sure next time he won't hit you.. :)

I think you can answer this for yourself. He has a girlfriend & he is way older as you say. He needs to grow up. If it gets more out of control, my only advice is to tell your friend whats been happening and that you've been trying to ignore him. She should understand.