OP ignore the people telling you what you should and shouldn't have known or done four years ago, they are hardly helping!
I do agree that your husband is unlikely ever to treat you well even if you change his mind this time. Ho appears to see women as something to be used and not as partners. That is always going to be lonely.
I think what might slow things down, and if not,at least get a better outcome for you and your children, is for you, your family, and the Imam to persuade your husband and his family to behave in a less shameful way, and to continue to support the children and ensure you are secure financially.
I would hope an Imam would be able to influence him and his family to look after you. But in the end, married or not, if someone decides to end a relationship then they can. And a few minutes on mumsnet shows that people (and most definitely men) do do this, even when thwy are married.
The main difference between your situation and a marriage recognised in uk law is that there is more chance of the abandoned spouse claiming a share of any joint assets for her/him self (though as pps have said, you will atill be owed child maintenance).
"Legal" marriage does not protect people against their spouses leaving - on the very same day they decide to go, in some cases .