If you have ever sat with the aftermath of infidelity and tried to understand how it keeps happening, you may have arrived at a question that feels both important and uncomfortable: why does something that costs so much keep feeling, in the moments before it happens, like something you cannot not do?

The answer is not found in your character. It is not found in how much you love your partner, or how seriously you take commitment, or how clearly you understand the consequences of your behaviour. The answer is found in the brain, and specifically in the way the brain's reward system builds patterns of compulsion that operate largely outside of conscious control.