I'm so sorry you are going through this.
I know the 'there's another woman' stuff must feel like a pile on but I think people are trying to prepare you. And another woman can just mean head turning rather than a full blown affair but in more cases than not, there is an idea of a life with someone else even if they haven't done anything yet (sorry).
I would recommend reading The Script. Not as some kind of gotcha he must be doing the dirty but to give you an understanding of where men go when it reaches this stage.
Dealing with the icy cold demeanor and the rewriting of your shared history, especially as it covers the whole of your adult life, is going to be tough.
Having a bit of insight into this pattern of behaviour might help you get through it, although it won't feel that way now.
Similarly the advice about photographing paper work, pensions documents, bank statements etc is good. You won't want to feel he'll turn but he's not in your corner any more, hard as that is to hear.
There is a window of guilt in which most men are more amenable before the shutters come down and getting things done in this period is useful. The money in the joint account can be used for your legal advice - and you need it. Can't afford it it's an option.
Look at online benefit calculators like Turn to Us. The process can be started even if he's not moved out.
Most importantly, remember you count too. He can end the relationship but he doesn't get the unilateral say in how he does that. Once you are past the initial shock you need to have a think about what you want to happen (I realise it's not want but how do you need to move forward)?