whatdidido, I thought I would just offer my thoughts on what I'd like my wife to do if OM were calling back.
I would like for her to tell me and then let me help her deal with it. You can make your H feel that you need his help to deal with the OM. It will both re-enforce your commitment to your H and let him have some say in how to handle the problem.
Wouldn't your R be stronger if you did not have any secrets between you? The OM is a problem for you both.