What happens to someone when they cant be themselves for a long period of time?

Kid has divorced parents. Grows up with caring familu on moms side until 11 years old. Moves to his fathers with his half sister and brother and stepmom. Could not act like himself for the 5 years he's with them until he moves back too his moms. Now my nephew is awkward and can't talk to girls like he used to. What happened to my nephew? He's back home in the environment where he's comfortable. being himself. He's not the same kid. How can we help him?