I honestly don't think you have much choice in this OP. Why would you want to carry on 'being nice' to this arsehole, do you honestly think that he's actually going to pay you back the money that you say you've lost?
He's been abusing you for years, and he will just carry on abusing you, so I really don't think you can win here, and if the house is being re-possessed, presumably he's either chosen not to pay the mortgage, or he doesn't have the money to do so. I would imagine it's the latter, as no one in their right mind would allow their home to be repossessed, if they were in a position to keep paying.
You still haven't explained about the property where you say, he's taken his clothes to. You said that you own a flat 'up North', but if he's gone to another property of yours, then is this another place that he owns, that you have no claim on?
If your current home is being repossessed, where are you planning to live? Much as I hate to say it, it's time to face up to what's going on. I know you don't want to go to the flat that you own, but I don't think you will have any choice, as the Council aren't going to re-home you, if you already own property. It sounds to me like you need some legal advice, as if you've been together for 25 years, you may have some sort of claim against him, but obviously you haven't really told us very much, so it's hard to know. Maybe book an appointment with Citizen's Advice as a starting point, and see what they suggest.