From your description, it appears your boyfriend has ended the relationship because you have prioritized your family above him. However, he has gone to such an extreme in insulting you in such a manner considering you've been in the relationship for 20 years.
Don't respond in anger nor use abusive words as a retaliation or to give him a piece of your mind. Let him know you've pondered on his text the reason you've taken time in responding. Let him know even though you're in a relationship, you can't ignore your family as they are part of your life as he is.
I know you're hurting considering how long you've been together. However, for him to throw such insulting words at you shows he lacks respect for you. If you would like to get back with him or not, let him know you'll accept his proposal that you won't call or text him. It will be hard to restrain yourself from contacting him but in time you'll get used to it.
Don't write a long text. Be brief. Tell him even though he has insulted you, you won't retaliate in anger or insult him. If he doesn't want to be with you it's alright. In time you'll find your foot though your enjoyed your time together. Wish him all the best and thank him for the things you shared together.