Q.Recently my husband of 40 years said he is leaving me, that there is no other woman and that he was going to live with his mother. He's 63 years old and I'm 60.

His reasons: I didn't hang his shirts properly or start the car right, didn't initiate sex or give him enough sex, etc. He claims he's been thinking of leaving for at least five years.

Two psychologists say he's going through a 'mid-life crisis' rather late. He's impotent and thinks himself a charmer with women.

I still have three children at home, ages 21, 24 and 28. I hold a fulltime job and recently was very ill, although I am fully recuperated now. But I can't cope with the situation, even at work. If I let my mind wander I get very depressed, although my psychologist claims I'm doing well.

Should I quit my job? I'm basically a homebody; I only went to work 10 years ago to help him out financially.

He has an 85-year-old mother who drives everyone crazy. One minute she's the sweet little old lady, the next a witch. I've offered to take her in. He says he'll send her to me but he still won't stay.

How do I put my life together? Where can I find material to read on the subject? Should I wait this out for a few years or go legal? A.A. You married for better or A. worse and now the worst has come. Your husband may think he doesn't love you any more, but surely it's himself he doesn't love.

Here he is, 63 years old, and he's got a problem: He's impotent. He can blame it on you, he can tell himself (and you) that he's a charmer, he can spend his spare time with the guys or go live with his mother, but the bottom line is this: he thinks he's over the hill.

There's nothing like impotence to make a man feel unmanly. And unhappy. And unlovable.

Impotence has many causes and none of them have anything to do with the way a wife hangs up her husband's shirts. It is a symptom of a physical or psychological problem and it is his problem, not yours.

When the body is ill the reproductive system is one of the first things to go. Sometimes diabetes is the cause or a high blood pressure medicine, lower levels of the male hormone, overdrinking (alcohol is harder to tolerate as we get older), or simply an ailment that's gone untreated.

Or a man may be afraid that sex will make an illness worse -- either his own or his wife's, or he may be frightened by the specter of old age, turned off by the symptoms of his wife's menopause or embarrassed by his own unexpectedly poor performance.

Your husband's drastic personality change is another sign that he needs a full physical check-up. The possibility that he is unwell, either physically or emotionally or both, is too serious for you to consider divorce yet.

Obviously, you're both too upset to hear what each other's really saying, but you have three friends who can intercede. Ask your children for their help; you can do it without talking about your sex problems.

Have them insist that he see a board-certified internist. Once this appointment is made, make an earlier one for yourself to tell the doctor about his symptoms so he can order the right tests and make a better diagnosis.

The work-up will also satisfy your own sense of commitment. Imagine how bad you would feel if you ended this long-time marriage, only to find he really needed you to stay with him, in sickness and in health.

Psychological problems are more likely. He's not only near retirement -- a critical time -- but he has just endured the stress of your own serious illness. The threat of death breaking up a deep and long-term relationship can cause a dreadful anticipatory grief and with it, fury. He could be subconsciously saying, "If anyone's going to leave, I'll go first."

You'll find his sexual problems addressed in the well-respected Sexual Turning Points by Lorna J. Sarrel, MSW, and Philip M. Sarrel, M.D. (MacMillan, $14.95). It contains good information on sex therapy, too.

You'll also want to read Giving Time a Chance, by Ronna Romney and Beppie Harrison (Bantam; $3.95). It will help you realize that the marriage that lasts has always weathered some big storms.

There are a couple of other good books, published by Thomas More Press, that your bookseller can order. One is Living Through Personal Crisis by Ann Kaiser Stearns ($6.95), who will walk you through grief of all kinds. The other is Your Aging Parents by John Deedy ($7.95).

It may not be fatal to bring his mother into your home, but it sure would be depressing. Even a caring husband isn't enough to help with a half-time witch.

If you're not going to get any love from him, at least for a while, you'll have to give it to yourself by keeping as busy as you can. Do it by seeing the therapist, staying on your job, joining a class, taking daily exercise, going out with the girls and occasionally treating yourself to a few days alone.

And if you have any love to spare, give it to your husband of 40 years. He sounds like he needs it.

Questions may be sent to P.O. Box 15310, Washington D.C. 20003