Sorry I didn't see your quandary until now, but I think you handled it very well. It's important to be able to state your boundaries and stick to them. Missher's analogy of the combatant putting down the gun first is very good. Now you need to see that she will meet your actions.
On the other hand, I do want to warn you that some of these OM who go around "stealing" wives are clingy, messed up types. Not to say they all are. But sometimes, they are not people who take rejection well. I'm not sure that you should butt completely out of her business of ending it if he is the clingy, "you can't leave me" type. Just let her know that if there is trouble with him, she can count on you to back her up. After all, she is still your wife, and if things go sour, he might need a man to explain it to him. I know this sounds soap opera-ish, but stranger things have happened!
