Q: This summer past, I had the misfortune to meet the young woman who a friend--that I consider a son--was interested in.

As a result of our meeting and my reaction to her behavior, a friendship that means much to me is mutually ended. I would have been wiser to say nothing, but knowing the adverse consequences of my thwarting this new relationship, I spoke out. What would you suggest to repair the estrangement?

My young friend had the privilege of using my beach apartment without charge whenever he wished. My previous experiences with both his female and male friends have been pleasant. I like his living habits, values and standards, and his other friends. His former girlfriend and I remain friends.

Last spring, he met another woman. In the months that followed, he dropped out of college, took another job to continue his schooling at night, and shifted his career patterns and investments, all due to this new roommate.

I expected the new girlfriend to be as gracious as her predecessor. I invited my friend to bring her for dinner. She knew that I would be there only for that evening. She also knew that they would have the use of my apartment for the next four days, and as often as they wanted it throughout the summer. And she knew what was being served.

They arrived. She advised me that she had a strep throat. She wore a swimsuit. She said she didn't care for the main dish and barely touched anything. While dining, she remarked what a lush my friend is! He drinks little--or, at least he did in the five years I'd known him. She was obviously bored.

I immediately inquired of her how they met. Her startling response was that she thought he was a "creep" when she first met him where he worked, and that he is the only date she has had who shaves his body (he is a swimmer, and most do it).

When he went to change so they could go out, she remarked, after talking about herself for a while, that he certainly takes forever in the bathroom. She was dreadful!

I have entertained, and been entertained, for 25 years, and I have never encountered such a rude guest. She is gorgeous, intelligent and knows it, and expects compliments for simply being there. She attended both a girls' finishing school and college.

I disagreed silently with her opinions of my friend and was shocked at her open rudeness. I left the next morning and said nothing. He told me later that he was in love, as was obvious, and intended to marry her.

Four days later, I saw my friend and said the following: That I have indulged him in every way for five years, but this situation I could not bear. I revoked his beach-visiting privileges with this woman, permanently. I advised him that if she would behave this way to any friend of his in this situation, whenever he displeased her, she'd let him know it long and loud in front of whomever--his family, other friends. I was appalled at her ridiculing him, and her behavior in general.

What I said came to pass. They ended the relationship. She gave him a bad time. I have tried to rekindle our friendship, but without success.

This estrangement is, to me, like losing a son. He is aware of my feelings.

What suggestions would you have? I was prepared to like her and to be as cordial to her as I have been to him. If my hospitality is so unappreciated and taken for granted, should I continue it, or simply shift interest and emphasis to other friends?

The woman's behavior, I concluded, was intentional and deliberate, to embarrass him and anger me.

A: Had you applied earlier, Miss Manners would have told you, with some regret at the illogic of it all, that one can never win by expressing distaste for the beloved of someone for whom you care. Even, as in this case, when the besotted lover himself discovers the mistake, he will persist in associating the person who discovered it first with his humiliation.

Try what you can to remove this mistake of having been right, retroactively. Saying "I understand how you fell for her, she certainly was beautiful"--if you can manage to choke the words out--may do what "I told you so" never will.

Feeling incorrect? Address your etiquette questions (in black or blue-black ink on white writing paper) to Miss Manners, in care of this newspaper. copyright (c) 1983, United Feature Syndicate, Inc.