Most Helpful Guy
Relationships are about compromises. Maybe not grow your hair to your butt, but out to your shoulders. It's not like he's asking for you to completely change your personality, he's just asking to not look less attractive to him. You would probably expect the same out of him.
Most Helpful Girl
Do what you want!!! Like Jesus Christ who gets upset about their partner doing what they want with their OWN body? It's HAIR.
If he can't handle you doing what YOU want with YOUR hair what else can he not handle you doing on your own. Seriously OP this is beyond ridiculous that he would even have an opinion on what YOU do with YOUR body.