How can I keep my dog away from someone that lives with me? I have a german Shepherd and he's extremely hardheaded.?

Just do it...........or move. Stop blaming the dog if that is who you're referring to as being "hardheaded" your responsibility to train it, if you're referring to your roommate, one of you needs to move.

For 'hard headed' read 'poorly trained'. If you rub your hands vigorously on the back of your friend's hands and allow the dog to sniff their hand it should have a placating effect. Repeat this a few times and the dog should accept your friend as part of the family and even guard him/her accordingly. Get your friend to take the dog for walks too as this will cement the bond. If all of this is done slowly and patiently the GSD will acquiesce. Guaranteed.

A hands-free leash can work well.

You TRAIN THEM or tell your idiot roommate to stay away from your dog then you move out since you're the one with the untrained, unsocialized mutt.

Put up a baby gate and confine the dog to your room.