HI @beingtakenforafool .. so sorry to hear what you are going through. Must have been a horrible shock. but lots of good advice on here about seeing solicitor etc.
Just to add, I can't see someone dropping the I'm walking out bomb, and I've been thinking about this for six months too, without having any idea of where they are going next and sleeping on the sofa.
I think this is a ploy to gain sympathy, to hang around to see what your reaction is after the first conversation, maybe to get your DC feeling sorry for him, the "I'll sleep in my car if I have to comments" really make me think that, and maybe even to get hold of his documents if you pop out or go to work as you say you've done all the financials. And then he can make the grand gesture of leaving the house etc.
Or he could be staying on the sofa so that he can make YOU take the decision that he has to go.. and can say.. "It's so unfair, she kicked me out. Poor poor innocent me "etc... I had to sleep in my car (because she is wicked of course)
But I don't think he does have no where to go, or has no plans for what he's going to do next, he's already said he's been thinking it for six months ( whilst lying to you!)
Having said that, I think its in your best interests to get him out as soon as possible and let him wonder about what you will do next... don't give any indication. I'm betting that there's a lot more to this story than he's told you that will come out in the wash.
But, you have your lovely DC and you sound like a kind and loving sensible person who will get through this. He sounds like a fool, not you.