Q: I recently broke off a three-year relationship — and his mother is my best friend. Who tells her and how do we do it?
A: A couple of red flags, here. First, if you are like every other woman I know, you have told your "best friend" just about every detail of your relationship, therefore, if your ex's mother is truly your "best friend" she already knows you and her son were having troubles and she will not be surprised at the news that you have broken up. If she is surprised, I'd be surprised.
According to good ex-etiquette, the best approach to dealing with conflict is to be honest and straightforward (ex-etiquette rule No. 8). This means you tell the truth when you tell her about the break-up. Whatever the reason.
It is not good ex-etiquette to volunteer specific intimacies that could be embarrassing to either you or he — or her (she IS his mother) if she's hearing intimate observations about her son.
If you broke up because either of you betrayed the other, that's a difficult pill to offer to your boyfriend's mother, even if she is your best friend. It means you betrayed her son, or he betrayed you and both would be difficult for her to hear — but you still have to be honest. If it was you, own it and express remorse for your bad choices. If it was him, he must also appear remorseful for the same. If he was the wrong-doer, let her be the one to vent about what a son of a gun he is. You say it, and it could end your friendship. And, if she does acknowledge his wrongdoing, be careful how heartily you agree. Utilize tact and timing — an unwritten rule to good ex-etiquette.
Finally, if she doesn't know, who tells her? My first suggestion is both of you together. If that is impossible, then it would be her son. If he's skipped town, then it would be you.