First of all, D is not final unless one of you see it that way. My dad remarried my step mom... after a few years of separation.
Secondly, there are ways to protect yourself from the other financially. There is the "innocent spouse" assumption the IRS holds, for instance. D is not needed to stop financial protection. There are stopgaps in place b/c in many M's one spouse is detrimental to the financial health of the M.