Case. The new spouse feels like an outsider next to the partner’s child from a past marriage.
Model. A module with a priority that can’t be lowered (the child) was added, and the new node competes for resources. It’s a priority conflict, not a lack of love.
What helped. They protected “the two of us” as a separate loop and didn’t make the child choose. Jealousy was named as a need for attention.
Lesson. The child is not a rival; rivalry comes from a shortage of the couple’s own time.
See Stepchildren.