You are not only married to a person. You are married to a nervous system — and so is your spouse. Four chemicals explain a surprising amount of what happens in your kitchen at 9 p.m.

Dopamine drives pursuit and reward. When it is high, your spouse is fascinating. When it drops, boredom masquerades as incompatibility.

Oxytocin is the bonding molecule, released through touch, eye contact, and shared vulnerability. It is the reason a six-second hug can defuse an argument that words could not.

Serotonin governs mood stability and the sense that things are fundamentally okay. Low serotonin turns small irritations into evidence of a failing marriage.

Cortisol is the stress hormone, and it is the one most marriages underestimate. Under cortisol, the brain narrows: your spouse stops being your teammate and starts looking like a threat. Most 'character flaws' couples describe to us are actually cortisol behavior.

The practical move is simple. Before you address the issue, address the state. Lower the cortisol — walk, breathe, wait twenty minutes, touch — then have the conversation. You cannot reason with a body that thinks it is in danger.