Q: My ex and I were together for 10 years. Over the years his sister and I became best friends, plus she does my hair. He cheated and I left and now he expects his sister and me to stop being friends and he wants her to stop doing my hair.

We think he’s ridiculous and both of us have told him no. He’s furious and making everyone’s life miserable — and he’s not even with the woman he cheated with. With the holidays coming up we can only anticipate the worst. What’s good ex-etiquette?

A: When people break up, they often think their friends and family should line up on their side. Doesn’t matter who is at fault. No matter how wrong they are, they expect allegiance.

Problem is, like you, friends and family often form close bonds with their family member’s partner and over the years the essence of the relationship stops being dependent on the family member. Then there’s a breakup and the family member start pulling rank. “You’re MY family and you should be on MY side.” Allegiances are truly tested.

Of course, we all understand how your ex feels, but he cheated, that’s the primary reason you said you broke up. Therefore, it’s on him and he has no one to blame but himself. If he expects everyone to support him in his mistake, that’s bad ex-etiquette.

Doesn’t mean they don’t love him — just means they don’t agree with his choices and they believe the consequences are his. It’s the, “I love you, just don’t love what you did” sort of attitude. That’s good ex-etiquette. Would the relatives feel the same way if your ex was the one who was hurt? Probably not — and rightly so.

Truth is, it’s always your prerogative to break up with someone — but there’s a right way and a wrong way to do it. Sneaking around behind your partner’s back is the wrong way. Betrayal is difficult to get over, and good ex-etiquette does suggest you don’t hold grudges and are not spiteful if you must interact with an ex. Since you have no intention of unfriending your ex’s sister, you will probably interact now and then, particularly around the holidays. Set the example. Family members will follow your lead. Don’t make them choose. That’s very bad ex-etiquette.

Finally, I’m not surprised your ex is no longer with the woman he cheated with. Research points to only between 3 and 5 percent of affairs end in marriage. I suspect, however, that’s about the same percentage of success for finding another good hair stylist on such short notice.

Jann Blackstone is the founder of www.bonusfamilies.com