Husband wants to leave me and I’m devastated

[ThatCoralBiscuit]

Our marriage has not been great for a while. He prefers to sleep on the sofa and will watch porn than being with me. We have three children aged 19, 17 and 16. The middle child is seriously disabled, mute and does not do anything for herself. She is diagnosed as autistic.
if I try to initiate doing something together, he gets aggressive and shouts he wants to be left alone. He prefers to watch films on his iPad than be with me.
i found a text message to my older daughter with him telling her that I am bad at cooking and cleaning and after Christmas we will separate properly. I felt terrible that he is texting this to our daughter.
i don’t want to separate but I just want things back the way they used to be. I don’t know what I’ve done to make him hate me. I’ve been with him since I was 19, I am now 45 and worried for the future. I am crying every day as I’m surrounded by couples and happy families.
i don’t want to have a pretend Christmas knowing he is going to dump me the week after.
i don’t know what to do - I’m completely lost and friends and family are sick of me talking about it.
he will not agree to counselling. I have tried.

If he hates you it's because he hates women. Porn is notorious for making men more misogynistic. He sounds like a porn addict and there is usually no coming back from that.
He is not even the same person anymore after using so much porn. It literally changes the brain.
So I'm sorry to say that you aren't going to have what you used to have.
This marriage is massively unhealthy for you and you have to let it go. I know it's hard, but you won't regret leaving him. You will regret staying.

He’s a porn hound
A filthy selfish pig
try to come to terms with him leaving as it sounds as though you will be better without him

It's not her responsibility to try to figure this asshole out. He's supposed to talk to her about what is bothering him, but he only yells at her or ignores her. This is typical pornsick behaviour, so I doubt it's even about her. It doesn't even matter why, because there is no excusing such behaviour.

Wow he's really ground you down, when you're a hard working person who clearly cares and doesn't deserve this!
Despite 3 DCs, one with additional needs, you've been able to keep up a FT job and you are enthusiastic to make things better. You deserve respect, security and enjoyment not the rubbish behaviour you've received.
Time to shake things up OP and think where could you be in a year (moved out, single, meeting new people, less ground down!!).

Our family situation was similar to yours when my parents split, 3 kids similar ages to yours including one of us with complex needs and requiring care.
It didn't take us long to realise that our parents were much better off and happier without each other. It was the best move for our family as a whole as we got to see the best of our parents again, we weren't oblivious to the atmosphere at home.
A decade has passed since our parents split and unfortunately one of them has now passed on, with the remaining parent not having a robust support system in place to help with the disabled sibling which is currently taking its toll. Make sure you're getting a fair deal with the care division, you need time to find yourself again, you'll be okay!