After you text her that, she's gonna come back at you. Turn off your phone if it's too hard to deal with for the day or leave it out of sight. Don't fight her, ask for explanations, explain how you know - NOTHING!!!! Let her stew in what's she's created.
This is your answer. You don't HAVE to respond. So she comes back with an angry denial. So what? You don't have to justify or prove she's lying. You know the truth. She knows the truth. What's the point of arguing about it? What does it achieve? Moral victories aren't going to do you any good--they will actually WORSEN your situation--so get out of the mindset of trying to achieve them.
Control you. That's ALL you have in this mess, control of yourself. Stake out some healthy boundaries, decide what it is that YOU want and are willing to accept in this relationship and then STAND by them. This is about you. Not her. Not your M. You.
