TowelNumberTwo's post excavates your desperation very well.
@Sophia878 there is no magic therapy or pill that will stop your H from seeking to destroy you. He needs a personality transplant, and to date that solution to the problem of emotional and psychological abuse has proved impossible.
The only element of this situation that can be changed is you.
Your strength here is your ability to speak up on your own behalf, to state your boundaries, and you have put your money where your mouth is too - you have gone to your mother's. But as you have seen, he keeps on ignoring you, though you couldn't have been clearer in the last few days about the damage he is doing to the relationship and to you.
He wants to treat you as some being who has no feelings, no opinions, no right to respond, an emotional punchbag. You are dealing with someone who is emotionally and psychologically stunted. Nothing can change this. There is no secret way to get him to stop and change, that will be revealed to you if only you keep on plugging away, trying harder, waiting for the charmed moment. He is getting what he wants out of the relationship. It is the pleasure of dumping on you, making you suffer.
Continuing to demand your support at this point regardless of everything you have said and done in the last week is going to feel like a battering because that is what it is - he is completely disregarding your reality, your experience of him, and demanding that you perform a role that is all about him instead.
I strongly suggest that you stop responding to his texts. You have told him you are sad and concerned about his father. Nothing more needs to be added to that. Go quiet.
I suspect that in responding with assurances of support you are seeking to control his reaction, his judgement of you, and to maintain equilibrium in the relationship. The illusion that the victim can control the abuser is one that you need to let go of. The optimistic illusion that something you say or do will change him is not your friend - it is actually toxic to you. Let the chips fall where they may now. Let him rage. You are currently safe. You do not have to go back.
As for your mother - I am not really surprised she hasn't understood you. Our culture is very forgiving of men, and holds them to very low expectations of behaviour. Many women of past generations were socialised to treat men as big, dangerous babies and also to always set aside their own needs and cater to others, mainly men.
Maybe ask her to read these:
www.joinonelove.org/learn/emotional-abuse-really-means/
outofthefog.website/top-100-trait-blog/2015/11/4/emotional-abuse
Look around for other articles and ask her to read them and try hard to understand, because you are not exaggerating, or callous about your dying FIL, and you need her help and support for your desperate situation. Ask her to put you first. You deserve nothing less.
Please call Women's Aid - 0808 32000 247.
Leave a message, and they will get back to you. You can go on the WA website to find your local contact number too.