Dearseer, You Do Have a Book for Him?

Our next letter comes from c k, who is, whose pronouns are she her, and who is writing from the dead dad club. My boy friend is an only child and is now acting as his mother's sole caretaker and sole source of socialization. She will call him at all hours, expecting him to drop everything to help her with something. He has expressed to me on several occasions that he cannot mentally, emotionally or physically sustain this. Is it unreasonable of me to want him to have more boundaries with his mother or get additional help? Any advice you might have would be so useful.