You are not responsible for the MLCer's choices, actions, reactions, and behaviors. It is all on the MLCer. It isn't within your power to "prevent" this at all. All you can do is to set them free to work through their chit. Put the focus squarely on YOU and how you'd like to create your own life separate from the MLCer. And make so darn interesting that you'll have great stories to tell during cocktail parties!