Q. How many times have I sat at my breakfast table while some woman friend my age (47) has wept and said, "I never thought it would happen to me." And all the while I would be thinking, "Yes, but it really won't happen to me!"

Of course it has. My husband of 25 happy (I thought) years has left, maybe to come back when he's had his fill of "freedom," maybe not. The sad thing is that I still resent it when people make snide remarks about him to me. I know he's behaving like an idiot, but I have the habit of wanting to defend him, of being on his side against anyone who criticizes him.

But that's not what I wanted to ask about. I can't stop him from making a fool of himself now. But I want to know how to avoid behaving foolishly myself.

You see, while I've tried to be helpful to those women who've been crying at my table, and I always started out sympathetic, I found that after a while I began to resent them. I suppose this will come home to roost now, and people will treat me the way I'm sorry to say I have treated others -- first pledging support, and then gradually dropping them.

I can't tell you why, or exactly what it is. One friend of mine took to the bottle, but oddly enough, she is the one I still see, and she has her drinking more or less under control now. But there were others I really had been close friends with who became different, somehow, after their marriages broke up. I don't want this to happen to me. I haven't done anything wrong, and there is no reason I should lose my friends.

My sister-in-law (who thinks her brother has behaved disgracefully) counsels me to take the opportunity to think more of myself, have a good time, maybe even "have a fling." She says I've been devoting myself to others (my husband and my children who are now grown) all my life, and now's the time for me "to be selfish." I'm willing to try, but I don't know how to go about it. How can a woman who is gray-haired, a little stout, and used to being a reliable helpmate, compete in this modern world?

A. Easily. The world is crammed with people who do know how to be selfish, who have no trouble thinking of themselves all the time, and who are eagerly in search of good times and flings. How can they hope to compete with someone who has a life-long habit of being kind and unselfish?

Here are some things not to do. Perhaps you will recognize some of them as common symptons of divorce, which, exhibited by your friends, contributed to your decrease of interest and sympathy in them:

Do not over-draw on the amount of sympathy to which one is entitled at a difficult period of life. Even with close friends or women in similar positions, try to limit your complaints and be sure to accompany them with a semblance of true interest in the vicissitudes of the other person's life.

Beware not only of the bottle, but of the telephone, which many people reach for with the same desperation, and over-use with the same self-indulgence and sloppiness.

Do not bristle with eagerness to have that fling. The glitter in the eye that advertises sudden availability is not attractive.

Do not dye your hair. This is the first gesture of the newly unattached middle-aged woman and, like the ditto of the male, which is buying a red sports car, it does not have the dashing effect that is intended.

What should you do? Continue to be a warm and cheerful person (even if you have to fake it for a while), making your interest and experience available to a widening circle of acquaintances, without dwelling on immediate benefits to yourself. This should make you quite a rarity nowadays, and there will be those who will appreciate it.