I'm going to pretend to care for my friend
Why are you going to pretend to care for him?
I don't want him to cry in front of me
If your friend is in need and it sounds like he is if he is going to cry, then you should offer genuine support to him. It isn't appropriate to be dishonest about your feelings when you are with a friend. Your friend will likely tell when you are faking and it would make him feel even worse about his situation.
I need to say I'm his best friend even if I'm not. Does that make sense? I just can't explain it any better.
Caring needs to be honest. Otherwise it is a lie. Make sure you are in touch with your real feelings and just have a real friend-like attitude, it won't hurt you to think that way.