I can totally relate to it (though on my end, I was never asked to do the lie detection - although it may have escalated to it).
My parents intervened for me when I couldn't do it. So please, just end it somehow. It will only get worse.
Cut him off completely in all ways possible and then you'll know as to what you've missed out on during the time you spent holed up with him.
As for the statistics, I dunno but, I am pretty sure that he won't leave you. It will keep going on till your last breath if you don't end it yourself.