That is a bad situation right there! It was bad enough in a previous relationship when my ex would talk to mutual friends about her issues in our relationship, but having co-workers know your business?! HELL NO!
This has to stop, you need to explain it calmly, rationally and in a non-confrontational way. If it still isn't getting through you could give examples like 'how would you feel if i was talking to steve in accounts about how insecure you are about your small cock'
"Never make someone your priority, when to them you are only an option"