What are some signs that a therapist may have poor boundaries with their clients?

Failing to mention the client in supervision/consultation, out of fear the supervisor/consultant will advise return to ordinary healthy boundaries.

Routinely going over the time limit with certain patients, compromising the time for the next client.

Struggling with fantasies of deeper connections with clients, whether sexual or parental or other intense or intimate relationships beyond psychotherapy.

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Off the top of my ancient head:

Serious disappointment when the client cancels a session.

Disclosing feelings, fantasies, and experiences to the client in ways not related to the work the client is engaged in.

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Obsessing about clients outside of work hours.

General Introduction to Boundaries from Panahi Counseling:

Sense of competition with persons who are important in the client’s life.

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Session-expressed curiosities about client details not relevant to the therapy.

Eager anticipation (or anxious anticipation) of the next session in ways that distract.

Frequent phoning or texting of clients to “check up on them and make sure they’re OK.”

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These items can happen fleetingly, briefly, in any therapy, but if they’re frequent, it’s definitely time for the therapist to get some good, solid supervision/consultation.