Sounds like you handled the situation well. Calm and all business is the approach, and it sounds like you did that. Now, the hard part, enforcing the boundary you set if she tests you - and I will not be surprised if she does.
Great that you did not cave on her question about losing your respect for her. Gives her something to think about, and shows you will speak your mind truthfully.
On whether to contact OM, like Sara said, that's your call. Just be careful if your W pushes back on proving to you she ended whatever was going on. If OM is M'd, a short note letting him know you know and to stop ALL contact with your W, or you will let his W know.
Keep in mind, your W, not you, is the one who breached your trust. So, she has to earn your trust back. Without full transparency, not sure she's serious.
