Your friend is so lucky to have you. Just be there for him and support him. He'll try to be better for you because you're always there for him.
From someone that has the same issue. Thank you.
Unfortunately there is a link in some cases.
For example, a living one: a girl that lived in a nice family. Everything seemed right. But it wasn't, she was invalidated from childhood. Something would be called childhood emotional neglect. And for an Infj care is everything.
She grew up with it...