I am listening What starts it is her being upset about something.
This leads to her admitting that she wants to limit contact. Where I mess up is I say limit? How about no contact!?
I discussed with her this morning that we should only be focused on us
You're missing the point -- again -- Ox. It's not the CONTENT of the conversations about OM. It's the very EXISTENCE of them, with her husband!!!
Where you mess up is, not cutting the conversation off IMMEDIATELY, and telling her you WILL NOT talk about her boyfriend while you are still her husband, as it's disrespectful, hurtful and inappropriate.