Sorry that your here and yes you made several mistakes. But don't feel bad, because we have all been there. Next time she threatens to tell your daughter and to leave. Call her bluff. She knows that is your weakness and will continue to play on that, while sleeping with OM. If she does so, then you be there to tell D14 what W is up to.
Also you need to detach and let W move out if she wants to chase after this guy. What is thus worse that is going to happen? Is she going to continue to mess with OM? It's already happening. That seems to be the biggest bad reasoning from everyone here, including myself. She needs to experience actual loss to snap out of her fog. She has seen that she can disrespect you and go with it out of fear of losing your W. But the truth is that she is already lost.
I know these isn't easy, especially being so new at this. But it will save you a world of pain by distancing yourself. Being nice will not work whatsoever. The time to be nice has passed. Treat her cordial lile you would a neighbor and better yourself.
