Q. My younger sister and I are young adults. We are extremely close, and have many mutual friends. She is educated, attractive, successful, single, and often regarded as the type to take no nonsense from guys. I am sometimes regarded as the slightly overprotective older brother.

This past weekend we took a trip together, went out to bars, and split a hotel room.

I allowed a mutual friend to stay with us, because he had been drinking. This friend is known for his exploits with women.

I fell asleep rather quickly, but awoke after a few minutes to them engaging in extremely animated intercourse.

I was paralyzed, but left the room as soon as I could. I spent the rest of the night/morning on the street before texting my sister and telling her to have him leave immediately.

I feel regretful, betrayed, and utterly disrespected by both of them. I’ve had words with my sister and she has apologized, but none of it seems to help me process what I witnessed.

I feel I don’t know who she is anymore.

I’ve not yet said anything to my friend. They are both integral parts of my life (especially my sister) and I can’t imagine life without either of them.

I know alcohol played a part, but I was with them all evening and know they were both in control of their faculties, so I don’t accept that as an excuse. Am I overreacting? What can I do to get past this?

Traumatized

A. You have every right to feel disrespected, and you were — extremely. Among other indignities, you were basically forced to spend much of the night on the street.

However, you should examine your feelings of betrayal. Is it because your sister couldn’t see through your friend’s reputation and hooked up with him? Or is it because she does know and doesn’t care?

Do you feel betrayed because your friend can be a player with other people’s sisters, but not yours?

These two are consenting adults. They should have the right to engage sexually with one another without you feeling involved — or betrayed.

Their choice to have sex in front of you? I agree that this is extreme, traumatic, and very disrespectful. Your sister has apologized. Now you must confront your friend.

You will also have to rewire your ideals concerning your sister. This could ultimately be liberating for both of you.

Q. “Keeping My Name’’ thought it was sexist to be referred to as “Mrs. [husband’s last name]’’ when she had kept her given name after marriage. I can understand that.

Although I did not keep my given name after marriage, I am offended when a sister-in-law addresses mail to us as “The [husband’s full name] Family.’’

While this may have been customary 100 years ago, now it just sounds patriarchal.

It sounds to me like the addressees are husband and children, with the omission being fully intended.

Left Out

A. I have had a huge response to the letter from “Keeping My Name.’’ This shows how very important names are, and how sensitive people are if they are addressed by a name that isn’t theirs.

In the case of Keeping My Name, I pointed out that even though she never took her husband’s surname, she is, formally speaking, “Mrs. Husband’s Name,’’ i.e. “the wife of’’ her husband.

Yes, this is old-fashioned. And since there isn’t an equivalent term for “the husband of,’’ it does seem sexist.

According to a recent story in The New York Times, roughly 20 percent of women married in recent years have kept their names. (I am one of them.)

But if relatively few women are keeping their surnames post-marriage (let’s stop calling them “maiden’’ names), why do some of these same women not want to be addressed as “Mrs. Husband’s Name’’? I assume in your case it is because if you’ve already surrendered your last name, you would like to hold onto your own first name. You should mention this to your sister-in-law.

Q. “Upset’’ was mad at her mother-in-law for refusing to provide a recipe for an often-made dessert that was her husband’s favorite.

The solution is easy. Almost every recipe in the world is available on the Internet; Upset could have bypassed her mother-in-law’s rudeness completely by simply looking it up.

Fellow Cook

A. I assume this is what “Upset’’ probably did in the end. She was miffed that her mother-in-law was refusing to honor a fairly simple request.

Amy Dickinson can be reached at askamy@amydickinson.com.