Too often, affairs are seen as the outcome of random horniness – or just plain old nastiness.

That’s very rarely the case. When it comes to affairs, we spend far too long being incensed or secretive, and far too little time trying to understand.

In truth, affairs stem from a very fiddly aspect of our romantic psychology.

In our relationships with a partner, all of us need carefully calibrated mixtures of two different ingredients. We have A Need for Closeness and A Need for Distance.

We want, in part a Closeness where we can hug, touch, be cosy, intimate and entirely relaxed and at home with someone. We want them to know our thoughts and to wander freely in their minds too.

But we also need Distance enough not to feel cloyingly submerged, subsumed or owned by another. We want to retain a sense of freedom. We need a private room to which we alone have the key.

Any imbalances, towards Over- Closeness or Over- Distance, will prove catastrophic if left unaddressed.

In a relationship which threatens to lean perilously towards over-closeness, we can be driven to stray by a powerful urge to prove to ourselves that not everything we do and are is owned by the partner; that we remain desirable to the world and a going concern in and of ourselves. Going to bed with a new person might not be simply about lust: it’s about escaping the alarming feeling that one’s whole identity appears to be dissolving into the couple.

But too much distance can undermine fidelity no less powerfully. The distance reads like constant rejection: when we try to touch the partner, they move away or sigh. When we bring up something personal, they change the subject. We may end up having an affair, not because we don’t love the partner any more but precisely because we do – and yet the distance they appear to be imposing on us through their lack of engagement feels unendurable and humiliating. It’s the final irony that – if caught – we’ll be accused of not caring, when it was caring too much that might have inspired the whole mistaken escapade in the first place.

Tragically, two people almost never enter a relationship with the same needs for Distance and Closeness. That’s why in every couple, we invariably hear the accusation that one person is too ‘clingy’ and another is ‘cold’. These are unhelpfully vicious words for what are, at heart, just two different ways of feeling comfortable in love.

It’s therefore an early imperative in any relationship to work out what the relative needs for Distance and Closeness are, to air the disjuncture, not to get angry about it, and mutually and with good humour to apologise for one’s distinctive contribution to it. Only thus can we hope to ensure that the gap won’t lead – in an online chat, at a bar or at a conference – to a situation where only an affair feels like a plausible solution to the vexing problems of Distance and Closeness.