A man who is married or is in cohabitating relationship yet propositions to other women to become his mistress (you) and then pursues another woman (widow) isn’t the kind of man you need to waste your time on.

That’s only two women they you know of (you and a widow) but who knows how many others he either intents or is already screwing on the side.

Personally I’d be done with friendship that same day he propositioned to be “more than friends” while being with someone else. Decent people end relationships before pursuing others. Don’t waste your time on people with no decency