Q: My sister is getting married, and her fiancé has asked my ex to be his best man. My ex and I don't get along very well, and I have asked her fiancé to reconsider, but he refuses. I am also in the wedding party, as well as our children, ages 10 and 12. What can I do? What's good ex-etiquette?

A: Many divorced people feel as you do. They expect their relatives' allegiance after their breakup and, "If I don't get along with him, you can't, either."

Truth is, it's not that your sister or her fiancé don't love you or that they are siding with someone else. It's that they've formed a relationship with your ex over the years that's completely separate from their relationship with you.

Sometimes we have to stand back and look at why we are so offended. It may have something to do with expecting those you love to line up on your side. And when they don't, or at least to the degree that you want them to, it adds to the hurt of the breakup.

Your kids are 10 and 12, meaning your ex could have been in your relatives' lives for almost 15 years — maybe more. This is a perfect example of the breakup ripple effect. One person's relationship and breakup affects so many — and we expect everyone to line up on our side. But that's not always possible.

Plus, if we are "putting the children first" (Good Ex-etiquette Rule No. 1) and using the best interests of the children as the criteria for continued relationships, your sister and future brother-in-law understand the need to continue positive interaction for the sake of the kids.

Out of respect for the bride and the groom, everyone who attends should act like adults and be respectful. I suggest you all go light on the alcohol, though. Alcohol can loosen the inhibitions and the tongue. Your kids will be watching. And now more than ever is when the adults in the children's lives must set the example. That's good ex-etiquette.

Jann Blackstone is the founder of bonusfamilies.com.