DEAR ABBY: My mom turned 60 last month, and I hosted a party at her house for friends and family. As things were winding down, I took a break from cleaning up to look over the birthday cards from well-wishers that were displayed on a living room table. Among them was a big, gorgeous card from “Cassie,” a woman around my mother’s age, who I always thought was nothing more than an acquaintance.

As I read the message she had written inside, my jaw dropped. While not pornographic, her message made clear that she and Mom have an intimate physical relationship that has been going on for a while.

I have not discussed the card with Mom, but I suspect she knows I saw it. Lately, I have canceled our weekly lunches together. I don’t have anything against gays; I believe they are entitled to a love life just like the rest of us. But in this case, I can’t help but feel betrayed. Mom was married to Dad for 32 years, bore him three children and seemed happy. Was this all a lie?

My biggest concern is, if this relationship becomes permanent, how do I explain it to my children — or worse, my brothers, whose views are conservative and some might say bigoted. I can’t help but wonder if Mom left the card out so she could open a can of worms in my lap. How should I approach this? Please help!

— Dumbfounded daughter

DEAR DAUGHTER: Some people are bisexual, which means they can be attracted to people of both genders. Your mother may have had a very happy marriage, and then she met Cassie. If she is no longer with your father, it is not a “betrayal” of anyone.

Call your mother and arrange to get together. Tell her you saw the card. She may not have told you about her relationship with Cassie because she was afraid you would react as you have. IF they become a couple and your children ask questions (keep in mind, they may not ask), tell them the truth. As to making any announcements to your bigoted brothers, leave that up to your mother and resist the urge to be the town crier.

DEAR ABBY: I’m only 18. I know I have a lot to learn in life, but I need help. I’m madly in love with a guy who is “bipolar” about our relationship. One day he loves me and the next he doesn’t.

Today he said he needed some time alone because we’ve been together 24/7. I got all mad and started to go crazy. He’s not breaking up with me. I know he needs space, but I can’t bring myself to let him have it. I don’t want to lose him. Please help me figure out a way to stay with him.

— Got a good one in Missouri

DEAR GOT A GOOD ONE: If you want to keep your boyfriend, let him have his freedom. I know it sounds contradictory, but the harder you try to hang onto him, the more he will want to get away.

And by the way, while he’s enjoying his “space,” you should do exactly the same thing he is doing. If you isolate yourself, you will only become depressed, insecure and clingy, none of which are attractive traits.

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