My husband has a brain tumor that is terminal?

but how do you deal with the mother than is in complete denial and trying to demise your marriage so she has control agan...for instance he has a few weeks to live and he asks (hense his mother) I cant beleive you stay by yourself every night..I think you are out and about...how screwed up is that she wants our marriage to fail at this point terminal with weeks to go...and I have taken care of him for 6 months