Many people who come to therapy after a stormy relationship ask some version of the same question: why did I end up with someone like this again? The question sounds like a complaint against fate, but it hides something more useful — the intuition that partner choice isn’t random, and isn’t fully conscious.

Relationship psychology has long described the phenomenon of unconscious partner selection. It isn’t about the “type” we say we like — it’s a deeper match: two people recognise in each other something familiar, something that fits the inner relational world each of them formed much earlier. Sometimes that fit is healthy and mutually supportive. Sometimes two personality structures “lock together” in a way that repeats an old, painful pattern.

This article introduces a short series on living with a partner who has a demanding personality structure — borderline, narcissistic, or bipolar disorder. We start with the question that ties the whole series together: who attracts whom, and why.

Complementarity: “matching gaps”

A classic account from the object-relations tradition comes from Henry Dicks in Marital Tensions (1967). His observation: partners often pair up through unconscious complementarity — one of them carries and expresses what the other cannot let into their own awareness. Someone who fears their own dependency may bond with someone openly needy; someone who suppresses anger may pick a partner who gets angry “for both of them”.

The mechanism that holds this together is projective identification — unconsciously “placing” a feeling that’s hard to bear into the other person, then reacting to it in them. In couples with a demanding structure, this process can be very intense: partners begin to act out each other’s unprocessed roles, and it’s this invisible “choreography” that keeps them together, even when they’re openly suffering.

What each structure is looking for

Elinor Greenberg (Borderline, Narcissistic, and Schizoid Adaptations, 2016) organises this in a way that’s useful for thinking about couples. In her framework, each adaptation is organised around a different central need and a different core fear:

Put these needs side by side, and it becomes easier to understand why certain couples form so easily — and separate so painfully.

The most common pairings

Narcissistic and borderline. Probably the most-discussed pairing. Someone organised narcissistically needs someone who idealises them and reflects their worth back; someone organised at a borderline level can idealise intensely and cling wholeheartedly to closeness. At first it works like a lock and key. The problem is that both structures rely on splitting — a world divided into “all good” and “all bad”. When idealisation cracks, that same mechanism swings into sudden devaluation. We go further into this in the article on personality organization levels.

Narcissistic and the “echoist”. Craig Malkin (Rethinking Narcissism, 2015) introduced the concept of echoism — the opposite pole to narcissism. An echoist fears being a burden, is ashamed of their own needs, and feels safest as a “mirror” for someone else. This pairing can be remarkably stable — and costly: the echoist gradually disappears. More on this in the article on relationships with a narcissistic partner.

Anxious and avoidant (an attachment perspective). Someone with an anxious style and someone with an avoidant style form an anxious-avoidant trap: the harder one pulls closer, the more the other withdraws. It isn’t malice — it’s two different, learned ways of coping with the same fear of losing connection, described in the classic four-category model of adult attachment styles.¹

This is not fate — and it isn’t anyone’s “fault”

The fit works both ways. Both people find something in the arrangement, and both lose something — which is exactly why it’s so hard to leave. And because the pattern is unconscious, it can be made conscious — and what becomes conscious stops ruling from hiding. In the approach I work in (ISTDP), what matters isn’t so much the label we put on the partner, but what happens inside you when you’re close to someone: which feelings surface, what anxiety blocks them, and which defenses kick in. That’s where the lever for change lives — not in diagnosing the other person.

How to read the rest of the series

Four articles, each on a different side of the same dynamic. We repeat in every one of them: these are not tools for diagnosing your partner.

Support in Lisbon & online

We offer therapy in English, in person in Lisbon and online across Portugal, for individuals and couples navigating these dynamics.

1. Dicks, H. V. (1967). Marital Tensions.
2. Greenberg, E. (2016). Borderline, Narcissistic, and Schizoid Adaptations.
3. Malkin, C. (2015). Rethinking Narcissism.
4. Bartholomew, K., & Horowitz, L. M. (1991). Attachment styles among young adults: a test of a four-category model. Journal of Personality and Social Psychology, 63(2), 226–244. doi.org/10.1037/0022-3514.61.2.226

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