My first thought is that he has an attachment disorder arising from childhood. The thought would be that for whatever reason in his family of origin he did not develop a secure attachment with his mother. Instead, he became anxious about closeness because, in the past, closeness was associated with pain and/or with someone trying to engulf him, take over his life, stifle his individuality, run things so as to meet their own needs. This phenomenon is often seen when the parent(s) are highly narcissistic.

Does he speak with a therapist? If not, I think that therapy should be given serious consideration.