Dear Tineoidea,

“There was probably some unresolved anger in her, maybe anger at her brother which she falsely directed at you.”

Actually I don’t think that’s the case. What I noticed is that she started to mirror his behavior towards me and using the same tactics which were alien to her before.

I see. It’s like she became a different person. I’ve mentioned it several times that she said she doesn’t know who she was. Suddenly changing her behavior and even personality completely, from one extreme to another, can be related to borderline personality disorder (BDP). I am not an expert and wouldn’t like to “slap” diagnoses on people, so this is just a possibility. A part of the BDP, as I read, is that they are confused about their identity:

“Identity disturbance is a term used to describe incoherence, or inconsistency, in a person’s sense of identity. This could mean that a person’s goals, beliefs, and actions are constantly changing.

It could also be that the person takes on personality traits of people around them, as they struggle to have and maintain their own identity.

The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) describes identity disturbance as a “markedly and persistently unstable self-image or sense of self” and notes it is one of the key symptoms of borderline personality disorder (BPD).”

You say that she was behaving in one way with you, and then with him, she adopted his style and mannerism, as well as his way of thinking. So for example, when she was with you, she might have felt that the problems the two of you had were minor – because you said they were minor. With him, those same problems became huge – because he said they were huge. It’s like a child who doesn’t know to decide whether to cry or not after they fall – they first look at their mother to see her reaction. If the mother panics, the child starts crying. If the mother says it’s nothing and reassures the child, the child might not even start crying and keeps running around.

Anyway, this could be a possible explanation of the “flipping” that happened in her mind. If this is true, it’s a major issue and needs persistent therapy. Usually dialectical behavior therapy (DBT).

I’m not sure how to feel but things have been (very slowly) getting easier. For now I’m giving it plenty of time and not contacting her.

Good strategy…

I still can’t shake off the feeling that this development has been very wrong and there’s some sort of childish hope growing in me. I want to believe that she’ll have to fortitude to come back to herself and detach himself from him, so we can at the very least have a proper conversation like we used to.

This development was wrong but I think it was inevitable – something else would have triggered her to flip sooner or later. Your “friend” was the catalyst. If she has BDP, she won’t be a pleasant partner to live with – unless she undergoes therapy. The only weird thing is that you said her parents were “exemplary”, and it doesn’t really go hand in hand with someone developing BDP. So perhaps not everything was so peachy as she told you it was… or of course, BDP is not what she is suffering from. So please, take this with a grain of salt…