I've wondered about this for a long time, in my own life. I don't think my situation is quite the same as yours but I've had similar encounters with narcissistic people who shaped my life when I was young, and I still see shadows of their effects today.

My running theory is that what we normally think of as narcissistic behavior is actually a two-person behavioral complex. One person slips into a role where they take all the power. The other person slips into a role where they abdicate it to avoid punishment and conflict. Both roles have an influence on others after the initial toxic relationship is over.

In the initial relationship this happens because the first person, the narcissist, is wired in such a way that they refuse to accept any other outcome. They will beat (figuratively, or sometimes literally) their partner/victim into the passive shape that they want to see.

After the relationship is over, echoes of the initial relationship keep happening because the victim's new "shape" influences their motivations and expectations for future relationships. They have certain things they expect to see from a partner and unknowingly create a dynamic where the partner must step into that role in small ways in order to engage.

An example: a narcissist may train their victim, over time, to believe that any expression of anger from their victim is bad. The narcissist sees a threat to their control that must be dealt with, and so when their victim expresses anger, the narcissist feels like they have to drag out the root cause of it and dominate their victim so that the threat is resolved.

The survivor of a narcissistic relationship learns that expressing anger brings punishment. But since it's natural to feel anger, they can't extinguish it completely and just do a really good job of hiding it.

In the new post-narcissist relationship, a healthy partner can't believe that the survivor doesn't ever feel angry. When they catch small, subtle signs that the survivor is frustrated over something they try to drag it out into the open--not to dominate them, but because they were raised in an environment where anger was aired in small, non-toxic ways, leading to conflict resolution. When the survivor doesn't admit to the anger (either because they're hiding it or are genuinely unaware of it), this creates immense anxiety in the new partner and sets off a chain of behavior where they try to get to the root cause of the problem. The survivor sees a shadow of the narcissist in their new partner's behavior.

This is horrible on both partners. The survivor feels like they're dealing with the narcissist. The new partner feels like they're being painted as the narcissist by the expectations of their partner. They didn't want to dominate - they wanted to have a normal argument, the type that they would have had in the healthy environment where they were raised. One that resulted in compromise, and give-and-take, and that restored balance. Instead they're now looked at as a potential threat.

In a worst case scenario, the new partner will eventually get so frustrated with the survivor's behavior that they eventually stop trying to understand and adopt the attitude of "well... this person seems to need someone to pick at them a bit before they'll get this stuff out in the open. So I guess I'll pick. I'll just trust that they'll speak up if it's too much." That's the point where the new partner really starts looking like the original narcissist.

I think the important principle to take away here is that a lot of the behavior that we consider "narcissistic abuse" isn't really unique to narcissism. It's nominally healthy behavior, but the narcissist twists it into abuse by being absolutely egocentric and unyeilding in using it to dominate and control their victim and "win" the relationship.

So, arguments become abuse because the narcissist uses them to dominate instead of negotiate. Criticism becomes abuse because the narcissist uses it as a tool for manipulation and control, not edification. Silence becomes a tool for abuse. Anger becomes a tool for abuse. Withdrawal becomes a tool for abuse. Approval becomes a tool for abuse. Peace becomes a tool for abuse. Gratitude becomes a tool for abuse. Altruism becomes a tool for abuse. All of it does.

The survivor of a narcissistic relationship learns to become suspicious of all these tools of control and tries to avoid the conflict they perceive in them. But they can't, because they're normal and were never meant to be avoided. Instead what happens is the survivor draws out less-healthy versions of them from their partner beause they are so used to abdicating everything in a bid to avoid conflict. It's a tragedy because it means that the narcissist has left an imprint of themselves on the survivor even years after the relationship has been ended.