Q. I am asking this as a manners question after having giving due thought, you may be sure, to the other aspects of it. What I want to know is how, not what, to do this.

My husband is having an affair with a long-time friend of mine. I know this for a fact, although they do not know I know, and I intend to keep it that way. Bringing it out into the open would irrevocably damage, if not end, our marriage. I believe if I let it alone, he will get over it, and we can go on as before. She has told me, in the past, about many such affairs she has had, and I'm sure she is not serious about this one. He, on the other hand, has never done such a thing before. I'm sure I would have known if he had. She is very beautiful -- I don't mean just pretty -- and it happened that she threw a lot of business his way when he was in trouble with his firm. Gratitude, I imagine, got mixed up with other things, and there it is. I will say for him that he looks miserable.

Okay -- so how do I behave to him, and how do I behave to her? On the one hand, I don't want to let on that I know, for the reasons stated, but on the other hand, I am no saint, and if I could speed along the end of this by making both of them really miserable, I wouldn't be sorry to do this. They see each other two nights a week and every other Saturday -- he is "working late" then, and she keeps her phone off the hook.

The only other person who knows about this is my sister, who has suggested that I openly have an affair myself, which would serve them right. However, even if I knew someone I wanted to do that with, I don't want to leave the children (3, 7 and 10) with no stable parent at all -- although in all fairness, I know their father is devoted to them. Nor do I want to give him an "excuse."

I just want to go on as always, acting natural, but the problem is I can't act natural. So what do I do?

A. Miss Manners thinks you are quite right not to attempt to "act natural." Behavior natural to this situation would be quite ugly, and thus go against your interests. And yet the agitation produced by your awareness of the situation produces an energy higher than you would have if the situation were normal. The idea is to use this heightened emotion for an effect that would serve your interest, rather than betray them.

What makes people truly uncomfortable is not so much having what others lack, but lacking what others have. Allow Miss Manners to suggest a more subtle way than your sister's of making them jealous of what you are doing two nights a week and every other Saturday.

To him, you might let it be known that you and the children are immensely enjoying those free periods you have together. Plan pleasant family activities for that time -- building, baking, putting on a play together, or, if you must, even going to the zoo where all the divorced fathers are on Saturdays -- which they will babble to him about afterward, thus making him aware that the time he spends away is the most valuable and memorable part of their childhood.

To her, if you really want to be evil (and why not -- it will make you feel better), you might make vague statements with a radiant face that make her believe, without your saying so, that you are spending that same time period with a man who makes you look more thrilled than your husband apparently did. This will pique her; but she will mention it to your husband, to salve his conscience. He will know, from the children's testimony, that it is not true, so it will give him the idea that she has a dirty mind. It will also pique him. Two people in these states of mind are not going to enjoy themselves for very long.