You seem to be in danger of not seeing the wood for the trees as there is ABSOLUTELY NO REASON why 'you' should be racking up solicitors' costs or spending any time visting CABs or other agencies.
The fact is that you owe him precisely NOTHING and if he begs to differ, he can pay a solicitor to prove otherwise by providing evidence of all of the sums he has contributed to the purchase of, improvements to, and upkeep of what is rightfully, legally, and solely, your property.
Should he be foolish enough to attempt make any claim on you in law, you will have opportunity to counterclaim for the monies you have expended on him by virtue of supporting him at various periods throughout your relationship and setting him up in business, including the purchase of a van and other equipment and the previous purchase of the Mercedes that the ow he so enjoys swanning about in.
However, until such time as you receive a letter from his solicitor you are best advised to refuse to acknowledge that he has any claim on you and to not prejudice your position by making him any offer - not least because any offer you may magnaminously choose to make will inevitably be regarded by him as acknowledgement of his claim and as the opener to negotiations which will lead to increasing financial demands once he realises that you are an easy touch.
In the unlikely event that you receive a letter from a solicitor that he has consulted in this matter, report the content here where we can ensure that your initial and any subsequent replies will serve to rack up his lawyer's bill while costing you sod all.
You do realise that this has come about a) because of his sense of self-entitlement and b) because he has bigged himself up to the ow?
You may never discover exactly what tales he's told the ow, but you can be sure they will include stories of how he improved your life immeasurably while you dragged him down and the vast sums he spent on buying and renovating the very same house that you purchased with your own money.
If truth be told, I suspect that she's under the impression that, once he has prevailed on you to do the right thing by him and sell up, he'll walk away with half - if not more - of the proceeds of sale because this is what drink does to an already addled brain.
What with his van and the Merc and his own business, the poor cow ow is no doubt labouring under the misapprehension that she has landed herself a real catch. Of course, we are not so cruel as to speculate on her disillusionment when she realises that the only reason she caught him is that she bought into his hype - suffice it to say that the shit (namely, himself) will hit the fan when she achieves enlightenment.
Please don't make the mistake of thinking that you can handle this matter amicably. It can't be done and the only way you will bring him down from the cloud cuckoo land he is currently inhabiting is to use language that he will understand.
Phrases such as 'off you fuck', 'in your dreams', 'bring it on', 'see you in Court', should help to dispel some of the crap myths that he has created in his own head and that of the ow, and will also serve to put some much needed and long overdue lead in your pencil where he is concerned.
And, yet again for the umpteenth time, ffs change your locks. You said you got your keys back from him but who knows how many copies he or the ow has made? Far better to be safe than sorry as it is not unknown for those who believe they are blessed with divine right to take the law into their own hands and help themselves to the possessions of other - and insurance companies rarely entertain claims where there is no evidence of a break in.
Grow some, honey - and start getting goddam angry with this pathetic gobshite. His bluff and bluster is not worth the paper it has not yet been written on, and should it be put into print it will prove to be as worthless as he is.
You've got a life to be getting on with... don't waste any more of it on him and his delusions.