The key feature of Prisoner's Dilemma is that cooperation cannot be sustained at all without the threat of future punishment. I don't think most people think marriages are impossible to sustain without punishment.

Fwiw, marriage sounds more like a coordination game to me. Those are games where if others cooperate, you want to cooperate too, but if others defect, you want to defect too.

A healthy, balanced marriage is one in which cooperation is sustained in equilibrium by both parties, without needing any kind of future threat to sustain it.

An unhealthy couple that stays together could be one in which the relationship is only sustained through a greater future threat if either party defects.

There could also be unbalanced equilibria, in which both sides are incentivized to cooperate, but the utility is very tilted to one side of the relationship or another. In these cases, no-fault divorce laws and other such things could likely tilt the equilibrium from cooperation to defection.