This doesn’t sound like forgetting. It sounds like he’s testing you to see how much he can get away with, and because you’ve stood up to him, he’s using slapping and choking as a way to reimpose his authority. This is completely wrong, and an obvious red flag.
In any d/s relationship, the power resides with the submissive alone. Subs cede control and give their consent. Subs set the boundaries, not doms. A dom who is incapable of respecting their partner’s boundaries clearly does not respect the precious human being they’re playing with.
The worry here is that choking is very hazardous, and requires a conscientious partner who you can absolutely trust. I’d worry about any partner who seemed to care more about their own gratification than their partner’s legitimate safety concerns.
Boundaries exist to separate consensual play from abuse. You decide where that boundary is drawn. If he can not respect that, you are putting yourself in peril.
Please, stay safe.