My child uses my feelings against me: when should I worry?

Usually, yes. A child who discovers that one particular sentence reliably lands on you has found a lever, and reaching for it is ordinary, especially in adolescence. It is also genuinely horrible to be on the receiving end of. Both of those are true at once and neither cancels the other.

Testing where the soft spots are is part of how a child maps the separateness they have only recently worked out you have. Knowing that you have an inside arrives well before any skill for handling it carefully does. Most of the time what you're watching is the gap between those two things. Read from the other direction, when it's the parent doing it to the child, the same mechanism is what Brian Barber measured as guilt induction, one of six domains of psychological control.

Three axes, and what matters is all three together rather than a count of incidents.

1. Duration. A bad fortnight is a bad fortnight. Something running for months is a pattern.
2. Setting. Does it happen only with you, or also at school, with other adults, with friends? Behavior that travels is different information from behavior aimed at one person in one house.
3. Cost. Is it costing your child something, in friendships, in school, in how they see themselves?

The American Academy of Child and Adolescent Psychiatry's guidance is built on the same shape: it points parents toward problems that persist over an extended period, that get in the way at school or at home, and that other people in the child's life have also noticed.

Consulting one isn't a diagnosis and isn't a verdict on your family. A single conversation with a family therapist is much closer to asking a question than to beginning a treatment, and a good one will say plainly if there's nothing here to work on.

The more useful frame: once the pattern is less about your feelings and more about your child's difficulty with repair, you've left the territory this page covers. Sharing impact was never the tool for that. Teaching repair directly is a different job, and wanting help with it is not an overreaction.