An argument ends in five minutes and then camps in your head for five hours. Evict it.

Conflict comes in two lengths. There is the exchange itself, which is short, and the rerun afterwards, where you deliver every line you thought of too late to an audience of one. The second one does most of the damage, and the other person has usually stopped playing it hours ago.

Give the rerun a container. Ten minutes to think it through properly, write down the sentence you wish you had said, then physically go and do something else. If it keeps coming back, it matters enough to raise again tomorrow when you are both calm.