As the length of the affair increases, the probability that your wife will eventually find out converges to 1. The chances that you'll slip up somehow, or get inadvertently found out through some voicemail, missed call, something, are too high.
And when that happens, the results are as predictable as they are horrible.
So how does it make sense to start down this path, rather than go for an honorable divorce now?
It’s entirely possible that the whole thing is just overconfidence, and the people involved think they can beat the odds forever. Maybe they’re just that stupid.
But I think I’ve figured out an alternative.
What if the eventual inevitability of getting caught is the feature, not the bug?
Suppose the unfaithful partner wants to be out of the relationship, but suffers from hyperbolic discounting. Even someone who has grown bored with their partner will still find it painful to tell their husband or wife that they want a divorce. You are wrenching the heart of the person you once loved enough to declare a lifelong commitment to. You want to be free of them, but that doesn’t mean you’re not dreading the process of getting from here to there.
So what will you do if you’re a hyperbolic discounter? You’ll procrastinate. You’ll convince yourself that you’ll leave your wife next month, or next year. And somehow next year turns into this year, and it never happens.
In this view, embarking on an affair is a sign of wanting out eventually, but not having the courage to just end it then and there. The affair is thus a commitment to eventually end the marriage at some unknown point when you get discovered. It functions somewhat like the Thaler and Bernartzi ‘Save More Tomorrow’ plan, or the complaint to the police by a domestically abused woman in a no-drop jurisdiction. It’s the ‘Divorce More Tomorrow’ plan for those without the courage to tell their husband or wife that they want to leave.
The indefinite timeline for discovery is also a plus – a known date would cause a lot of stress as it approached, and would create the risk of massive preference reversals. The unknown aspect means in addition that the final choice is taken out of the cheater’s hands, which benefits those who want to feel like the divorce was the process of some inevitable deterioration in the relationship, rather than an active choice by them (we grew apart, things didn’t work out, the knife went in).
My guess is that when the cheater is eventually discovered in their lie, once the initial shock is overcome, the next feeling is relief. Relief that things are finally drawing to the conclusion that they’ve long wanted, but haven’t had the courage to actually ask for.
It seems a strange explanation, but I can’t think of a better one.