DEAR ABBY: Five years ago, my brother-in-law sent my sister “Rita” and me on an all-expense-paid weekend trip to Canada. He asked me to tell Rita that I had “won” it for outstanding performance at my job and wanted her to accompany me.

To make a long story short, it turned out he did it in order to cheat on my sister. Because we had problems with the arrangements he had made, Rita and I had to return a day early. When she opened her front door and walked in, she caught her husband red-handed.

Ever since that unfortunate incident, Rita has cut off our entire family. She acts as though WE cheated on her, and remains married to this despicable man even though he lives with the other woman.

I don’t understand why my sister has pushed away all of the people who love her while maintaining a relationship with a man who cheats on her. I don’t know what to do. Any advice? – MISSING MY SISTER

DEAR MISSING: Your sister may feel that she deserves the treatment she’s getting from her husband, or is still hoping that her wandering spouse will return. Because you were part of the deception, she has displaced the anger she should be aiming at her husband and has directed it at you because it is “safer.”

Until she finds the strength and courage to accept that her marriage is over, her behavior will probably continue. I’m advising you to go on with your life until she is ready to change hers.

DEAR ABBY: Most of my extended family are pleasant and enjoy each other’s company when we meet at family gatherings several times a year. But three of them (all from the same side of the family) are just plain rude. Every event becomes an uncomfortable exercise in bracing oneself for the verbal attacks that come from these critical, judgmental people.

We have tried talking about it, but hear the same refrains – “I’m not changing,” “Accept me as I am,” and, “You have no choice but to put up with me because we are family!”

I am a younger member of this family who occasionally spends holidays with friends or traveling. When I do, I am severely chastised by these three relatives, who say I have “no right” to skip family gatherings. If they were nicer people, I would want to spend more time with them.

I want to do the right thing, but what do people who have the same ancestry “owe” each other when there is no connection of friendship or goodwill? – RELATED IN NAME ONLY IN SAN JOSE, CALIF.

DEAR RELATED: I know of no rule of etiquette that states you are compelled to attend every family event. Good manners dictate that you treat those around you courteously. But that does not mean that you must engage in anything more than casual, superficial chit-chat with those who are critical, judgmental and rude.

Because these get-togethers involve extended family, spend the majority of your time with the relatives who make you feel welcome, supported and loved.

P.S. One thing you do NOT owe these folks is an explanation regarding your absence when you choose to avoid them.

Dear Abby is written by Abigail Van Buren, also known as Jeanne Phillips, and was founded by her mother, Pauline Phillips. Write Dear Abby at www.DearAbby.com or P.O. Box 69440, Los Angeles, CA 90069.