Could anyone talk me very slowly through how buying someone out of the house works?

[Helpagirlout222]

I hear people talking about this, and know people who have "bought their ex out of the house". Mainly as far as I know with large cash injections from family.
I don't think it's an option for me, but I'm clueless as to how it would work.
Ex-dh (separated, not divorced) and I have both paid the mortgage equally over many years. Unfortunately it's massive as we remortgaged to get work done on the house. However we still have some equity in the house.
I am in the house with the kids, and in an ideal world we'd stay here.
Could anyone explain how I even begin to work out what his share would be? In very simple terms?!
I know I'd need to get the house valued, then, work out the difference between what's left on the mortgage and the value of the house?
Utterly clueless. Any help very gratefully received!

Hopefully he means what he says.

Mine did. he said he wasn't prepared to support him and he hasn't. He sees not giving him any money as a positive thing in that he needs to learn to stand on his own feet. I don't completely disagree but essentially it was 1 year of uni to go at the point our finances separated and DS lives with his g/f so it wasn't just him to consider, there is her too in that if DS has no money then that impacts on her ability to pay their rent and bills as well as his.

Anyway, I used a broker for the mortgage as I'd initially just gone to First Direct who agreed a mortgage in principle up to age 80 and then kept me hanging for a month thinking all was good and then they came back and would only give me a 9 year mortgage rather than than the 23 they'd agreed to as they wouldn't use my SIPP as a form of income. A got the details of a broker from a friend going through the same thing. Did all the details over a call and email and post and he had me sorted with money all supplied in a matter of weeks. In the end I didn't get the 23 years I was originally looking at but i did get 18 which was affordable enough. The broker didn't take a fee either.