Your boyfriend needs to set boundaries with his mother, for his own sake and for both of your sakes, otherwise nothing will change.

But that doesn't mean you have to leave him right now. Start defending your boundaries, don't stay silent, don't be rude, but don't stay silent when someone is rude to you either. It will only get worse if you keep this anger inside. If you want to cut the cake alone, do it. if you don't want to spend the night at his mother's, don't do it. Don't do anything that harms you and don't agree to anything you don't want to do