Q. I have been told by a reliable source that my lover, with whom I have lived for three years, is interested in having an affair with another woman.

I am in deep etiquette trouble, because although I can see the outward signs of his inclination, I do not know about it officially. I am afraid of how I might act if I catch them together or if he tells me directly.

Though I have wanted to do so, I have not followed him around, gone through his wallet, tried to get more information on his activities, questioned him about where he was at what time, confronted him or exhibited other forms of low-class behavior.

I am in great emotional pain. What is the correct behavior for the wronged woman who is being deceived?

A. It would be tragic if you permitted your unhappiness to spoil your principled manners. There is never a greater need for etiquette than when the inclinations are understandably straining for something cruder.

Perhaps it will reinforce your resolution if Miss Manners points out that behaving better than you feel would not only be noble but smart. And violating your standards may do harm to your situation, as well as to your character.

When justified jealousy provokes what you call low behavior, it offers the deceiver comfort. It would take only one act of underhandedness to convince your lover that his deserting you would actually be prudent. You would, in effect, be giving him cause retroactively.

Behaving as if nothing has happened won't change the situation: On the contrary, someone looking for excuses will claim that as proof of insensitivity, saying that if you had real feeling for him, you would sense that something was wrong.

She is suggesting that you should demonstrate that you do have real feeling for him. An unexplained air of sad mystery will refocus his attention on you, if only because he will go crazy not knowing what you know.

Why go to so much trouble and delicacy for someone who is false? One reason is that he may not be: You may be mistaken in believing vicious gossip.

Failing that, she would like to point out that passing fancies often pass without any action being taken. You would not like to interrupt your lover's reflection that you are, after all, the finer person, by demonstrating that you are not.

But even if your fears should be confirmed, you would do well to maintain your dignity by expressing nothing but regret that something once beautiful is over. This will make anything your successor says to justify his action sound crude, and it will really doom her later, if her standard of behavior under even light stress is not as high as yours in a major crisis.

That is the kind of revenge available exclusively to the polite.

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