If your "caring" step-dad who is a "good man" has split with your mother, then I think you mom has issues that go far beyond a broken marriage and far beyon the expertise of us "laypersons" on this forum. I'm not trying to suggest that everything was your mother's fault but considering the high regard in which you seem to hold your step-dad, I can't help but wonder what could have caused their marriage to crumble? Your concern for your mother is certainly admirable but I think you've done everything you can for her. She needs help from the experts so encourage her to get it. Good luck!