Great Lesson Freshly Sane - thank you for sharing it here!
When I first read this, I realized my role and that I had been just as guilty of doing this to after a few years with my ex.

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I would start saying things like - what does your therapist say about this - rather than setting real boundaries.
NOW - triangulation
(read definition) is something I notice many people do and the way I handle it is to not let myself get involved... . well, most of the time

I am so happy to see you bringing the lessons in for discussion - kudos to you!