MCS, it is my role as your DB friend to support you as I hope so is yours for V. I really want your success and happiness however that ends for MCS. When MCS does the best he can, he should be proud, he can ask no more of himself.
W is truly wayward and MCS let her be. If she lies about you that may be a boundary issue for you. In this way W needs to know.
MCS, you could say 'W you and I know the truth about OM. If you continue to say X and Y about me and it is repeated to me then I will correct the lie.'
MCS have you seen Sandi new post about Wayward Wives, it is insightful reading MCS.