I discovered my family's adoption secret while snooping. Now I want to know more.

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Dear Prudence,
I'm a 21-year-old girl, and I live with my mother. We've had a rocky relationship, which has improved, though we're not close. My mother isn't very open about her past or her life in general. My parents divorced when I was a baby, and my sister and I didn't find out why (his drunkenness and infidelity) until about two years ago. I'm writing because of something I accidentally discovered a couple of days ago. I was staying home sick from work, and I looked in my mother's nightstand for her heating pad. There were a couple of envelopes with the return address of a religious charity. My mom is not the type to do charity work, so I was curious to learn this about my mother. I opened one. It was from the church's adoption clinic, saying they had received a request from my mother for information regarding the daughter she had put up for adoption. My mother had had a child while still in her teens. She filled in the form for more information but had never sent it in, so I don't believe she knows anything about this child, who would now be in her late 30s. I know it's none of my business, and I feel guilty for having read the letters. But now my sister and I, who are no longer children, feel that we have a right to know about our new older sister. How do I sit down and ask my mother about something I'm not even supposed to know?

—Waiting Sister

Dear Waiting,
You have committed such a violation of your mother's privacy that it's going to take a long time to regain her trust. Normally, I would say information gathered by opening envelopes in someone else's nightstand is of such a radioactive nature that it should be buried in the Yucca Mountain of your mind. People are entitled to their past and their secrets. However, I make a general exception when it comes to erasing the existence of another person who is a member of your family. Parents who have placed a child for adoption before beginning their current family should at some point let their children know about this sibling. How much better to tell what happened than to suddenly have a middle-aged person appear at the door looking for Mom. So now you know that somewhere out there in the world you have another sister, and I agree that secret can't be reburied. You and your sister need to sit down with your mother and, after offering an apology for how you found out, tell her you read the letters. Don't insist on your "rights." Instead, tell your mother the two of you love her and want to join and support her in this journey to find her other daughter.

—Prudie

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Dear Prudence,
My 18-year-old baby sister started college in the fall. She was always a very socially awkward child, didn't have many friends in high school, and had never been on a date. Though she is very smart and a talented artist, she also has some developmental issues that make her socially younger than her years. When she chose a large college 3,000 miles from home, we were all concerned. But it seemed like things were going well. She made some friends in the school's art community and was involved in a number of activities. Last week, however, she called and told me (with great excitement) that she was in her first relationship. I was happy for her, too, until she told me he is a 60-year-old she met at a community art class. My sister had never even kissed anyone before him, and now, with her so far from home, I am worried about her safety. What kind of man would be interested in such a young girl who has no relationship experience and is very young for her age? I told her I would come to visit, but what should I do in the meantime?

—Wary of Older Men

Dear Wary,
Based on what you've written, it's impossible to know if this guy is a sexual predator taking advantage of a developmentally delayed girl or if your sister is overinterpreting an odd but unconsummated friendship. You need to find out more about the nature of their relationship. If it appears he's a creep who's manipulating your sister, perhaps your whole family needs to come out for a visit. But this is a delicate mission. Your sister clearly felt she was ready to be on her own, and she has mostly made a success of it. You all want to celebrate her accomplishments while letting her know this man is wrong for her, if that's what the case turns out to be. And if she does lack the judgment to know how to protect herself, perhaps she would agree to have a family meeting with a campus counselor to discuss setting up a system so that she regularly checks in with someone who can help advise and monitor her.

—Prudie