C, you know the drill, sweetie, you keep saying the same words over and over and she hears, blah, blah, blah.
She knows how you feel about the OM. You've said it, she heard it, no need to say it again, right?
The thing about a boundary is that it has to be for you. It cannot be to punish the other person and the most important part of it is that if you set it, you have to be prepared to enforce it, Otherwise, it;s not going to be taken seriously.
So, shake it off, get back on the path, and do better next time.
