Choose your battles wisely. Is that really a breaking of trust (sounds more like a privacy issue)? W can't be expected to live having to check everything with you first. If telling a nosy coworker about the MC was to you a breaking of trust, talk to her about how you feel in a non-accusatory manner, validating and understanding what she's thinking. Don't bring up old issues or grudges! If to her it wasn't a matter of breaking trust, accept that her viewpoint and rationale is just as valid as yours, even if you don't necessarily agree with her perspective.
The best resolution is one where neither partner agrees to do or not do something that makes them feel like they've "lost" or as if they're a child. Work towards that.
