I'd be very careful about using "boundaries" to dictate the behavior of another person. I think it's possible to use them to influence their behavior, but not to outright control them. Wasn't there a boundary (in your use of the word) in your marriage to begin with about not engaging in extramarital relationships?!? What makes you think that a boundary line of this sort will be respected now? Boundaries (in my understanding in this sort of sitch) are more about what you will subject yourself to. If you set a line at phone calls, what will you do at this point? It's a fine line between controlling and protecting yourself.
Also, by setting boundaries regarding OM contact and interactions, your are implicitly condoning the A. You don't, do you?
“No problem can be solved from the same level of consciousness that created it. ” – Albert Einstein
