You've been used big time. He's not a nice person.
It also happened to me. Engaged to a man. His company went bankrupt. He moved into my new house, which I had just bought. He was so helpful with the sale, especially as I was working long hours and travelling for job.
Six months later he bought himself a home, which I was quite surprised about, as he'd only recently found a well paying job - and didn't have 6 months salary to show.
But absolutely flabbergasted that he sneakily bought it without me having an inkling that he was even looking for a house.
That ended all trust and the engagement.
It was only 7 years later, when I came to sell my home, that I found out he had put his name on the deeds as a co-owner. Mr so-helpful-with-the-house-sale and solicitor used my house as collateral for his new home. Moronic me signed the papers, where he asked me to sign - not realising what I was signing.
I am so glad I ended the engagement when I ended it. Right when all trust was gone. And at point where I could prove he did not contribute to my home or mortgage in any way.
He signed over "ownership" without fuss, because I would have taken him to court for fraud.
However, I would seek legal advice. If you supported him with free or low-cost accommodation for 10 years with the expectation that savings would go to a joint financial future - you may have a claim.
But if you've both been complicit in hiding the fact that he's been living with you, for the purpose of claiming benefits, you might find yourself in a whole stack of trouble.
Because your name alone is on the home you live in and your name alone is who the benefits are paid to. The authorities will come after you alone.