Demetrius never spent much time with his family, beyond his father's strict treatment for having good grades, typical Japanese problems.

Actually, he was never sociable. He had a few friends, one was you and others were your family, although practically you didn't count much considering that you are his partner and childhood friend.

Demetrius spent more time at your house than in his own house, but he never told you why. You suspect it is because family Issues, and you were not wrong.