Wasalam sister, I'm so sorry you're in this situation.
It sounds like your mental health is really affected, and mental health is just as important as physical health. Do you have access to specialist care for your mental health, like a psychiatrist or psychologist?
When you say you thought you would want this, was the pregnancy planned or hoped for? Do you think there are circumstances in which you would want to continue the pregnancy, eg if you had more support, or are you clear in your own mind that you can't continue it?
The legal process will depend on the country you're in, but Islamically, my understanding is that the major schools consider termination to be permissible/acceptable to save the life of the pregnant woman. Could you get a doctor or scholar to discuss this with your husband, considering the implications of this for your mental health, to get him to sign off on whatever you need him to approve? Your children still need you, and if this pregnancy presents a risk to your life then it would be a hard heart indeed to seek to force you to risk depriving your children of their mother.
Are there charitable organisations for women where you live? They may have ways to help, up to and including helping you travel elsewhere for healthcare.
This is a big decision, with implications for your mental health, physical health and family, whatever you choose, so I'd suggest praying for guidance and speaking with at least one female scholar. Do you have any female family members or friends in real life you could confide in? They may be able to give you their perspectives too, and potentially practical help.