A word to describe feeling less of an emotion

What is a verb and also a phrasal verb to describe to gradually feel less of an emotion (anger) over a period of time to the point of almost non-existent?

For example: John was ridiculed by Dave during class, making him want to punch Dave out, but at the time it was inconvenient to do so. By the time class is over his anger has already ___ and he no longer wanted to give him a beating.

dissipate: "(with reference to a feeling or emotion) disappear or cause to disappear"

In the context of your example (with some tense changes), especially when referring to anger, I would use "By the time class was over, his anger had already subsided".

I would say diminished or died out.

Dissipated works for this purpose. Merriam-Webster defines the word to mean "to cause to spread thin or scatter and gradually vanish." It's often used in reference to feelings and also to the loss of energy as in "the heat from the car dissipated after parking in the shade" or "his anger dissipated as the situation became clear."

I would say that abated fits here.