DEAR ABBY: I recently discovered that my fiance has been seeing another woman for the past year and a half. He swears that I am the one he loves, and he still wants us to get married. However, I'm having difficulty digesting all that has happened. To make matters worse, the other woman is pregnant.

What should I do? I love him, but will I be able to trust him? Should I marry him and live with the knowledge of his affair and love child for the rest of my life? -- DEVASTATED IN NEW YORK

DEAR DEVASTATED: I can't decide that for you. The question you must ask yourself is how will it affect you as your husband supports the child he fathered during your engagement, and your own ability to accept the child if your husband wants it to be part of your lives. After all, it's his flesh and blood.

Your fiance has committed a serious breach of trust, and you are right to question both his truthfulness and his ability to be monogamous. A relationship that has lasted a year and a half isn't a "fling" or a one-night stand. Proceed with caution.

DEAR ABBY: My wife and I are in our 20s and have the first grandchild on both sides of the family. Naturally, they all want to spend time with her. Because of a divorce/remarriage in the family, there are three sets of grandparents and two sets of great-grandparents. Some of them see her at least twice a week, the rest at least once a week.

Abby, my mother is offended that we asked another grandparent to baby-sit for us once. Another problem is a couple of the grandparents think our 5-month-old daughter should taste adult food. We have advice from nurses about our daughter's care, but the grandparents think they know better than us or the nurses.

We know that it is good for our child to know all her grandparents and that she is special to them, but we need time with her without them.

Please print our letter. Maybe they will recognize themselves, and then my wife will not have to feel guilty for no reason, and perhaps they will back off and let us parent our daughter without our having to move far away. -- YOUNG FATHER IN CANADA

DEAR YOUNG FATHER: With three sets of grandparents competing to see who will spend more time with the child, I don't blame you for feeling overwhelmed. Ignore any advice that conflicts with your pediatrician's -- and establish a strict schedule for them to see your daughter.

DEAR READERS: Today we celebrate the birth of a great American, Dr. Martin Luther King Jr., whose life was dedicated to furthering equality for those to whom it had been denied. His speech, which began, "I have a dream ..." is a classic.

However, another quote of Dr. King's bears repeating: "The good neighbor looks beyond the external accidents and discerns those inner qualities that make all men human, and therefore, brothers."

During this final year of the century, look into the hearts of your neighbors. It will reconfirm that despite our difference, we are all very much alike.

What teens need to know about sex, drugs, AIDS, and getting along with peers and parents is in "What Every Teen Should Know." To order, send a business-sized, self-addressed envelope, plus check or money order for $3.95 ($4.50 in Canada) to: Dear Abby, Teen Booklet, P.O. Box 447, Mount Morris, Ill. 61054-0447. (Postage is included.)

DEAR ABBY: During the holiday season, you often publish letters from older persons complaining about being alone or left out. Last winter, my husband and I entertained six sets of overnight guests at our Florida home. Most of them were over 65. Based upon our experience, here is a questionnaire for the person who hasn't received another invitation:

(1) When you arrived, did you greet the host and hostess warmly -- or did you complain about the airline, the stairs, the driveway, the distance, the traffic and the crowds?

(2) If you have special dietary requirements, did you inform your hosts well in advance, or did you wait until the meal was on the table? Did you expect everyone to eat only your special diet?

(3) Did you talk about anything other than your medical problems? Did you show an interest in others and ask questions about their lives?

(4) Did you complain that the bed was too hard or too soft, and if the pillow was not to your liking, did you feel compelled to say so?

(5) Did you claim the best chair in the house as yours for the entire visit? Did you complain about the weather? Did you adjust the thermostat to your comfort level without first asking your hosts?

(6) If you are early to bed and early to rise, did you expect the entire household to conform to your schedule?

(7) Did you state your opinion and give advice on every topic? Or did you consider the fact that others may know something, too?

(8) Did you express gratitude for the efforts your hosts made on your behalf?

Abby, our reason for inviting guests is to enjoy their company. What causes some people to think they no longer need to practice good manners simply because they are older? -- INVITING FEWER PEOPLE TO FLORIDA THIS YEAR

DEAR INVITING: Your frustration with houseguests is reflected in your questions. Good manners are essential at any age. It is as important to be a good guest as it is to be a gracious host.

You may appreciate the following "Caution to Houseguests" submitted by Nita Skidmore. It appeared in my column a few years ago.

CAUTION TO HOUSEGUESTS

(1) Open all closet doors and drawers with caution.

(2) Do not move any heavy furniture -- there may be dirt.

(3) Don't draw your finger across any picture frame. (We rarely dust.)

(4) Do not open the box under the kitchen table. (That's where we keep Grandma's ashes.)

(5) Don't be afraid to use a clean towel and washcloth. We have plenty. (As you can see, we have traveled a lot.)

(6) If you take a book from the shelf, beware of moths and bookworms.

(7) Don't bother looking under any bed -- there's not room enough for a man.

(8) Please sit down very carefully -- the cat might be there.

(9) If you should find a long hair, give it back to me; I need them all.

(10) Feel free to help yourselves to anything you find in the fridge. It's always too full anyway.

(11) Do not remove the toilet paper from the bathroom sink -- it's our solution to the leaky faucet.

(12) Don't ask why the dragonflies fly only in the side yard. Nobody knows.

Everybody has a problem. What's yours? Get it off your chest by writing to Dear Abby, P.O. Box 69440, Los Angeles, Calif. 90069. For a personal reply, please enclose a stamped, self-addressed envelope.

DEAR ABBY: This is in response to "Hurt Mom in Washington," who was both angry and sad at her daughter's wedding plans. I was in a similar situation five years ago when my daughter married. She, too, insisted on planning every last detail of her wedding on her own, and made it more than just a bit clear that she was going to do things "her way" without any "interference" on my part.

To make a long story short, several weeks before her wedding her caterer informed her that due to a scheduling misunderstanding, he would be unable to cater her wedding after all. After frantically contacting many other caterers without success, guess who she asked to cater the wedding? You guessed right -- good old Mom!

Although I wouldn't want "Hurt Mom's" daughter's plans to go awry, she needs to know that these things usually have a way of working themselves out.

The food I prepared for my daughter's wedding turned out so well that some guests had a hard time believing the reception had not been professionally catered. It also helped my daughter and me regain the closeness we had previously shared and enjoyed. Sign me ... BEEN THERE IN WASHINGTON

DEAR BEEN THERE: Your daughter was fortunate to have such a talented and forgiving mother. Your experience gives new meaning to the slogan, "Nothin' says lovin' like something from the oven!"

DEAR ABBY: I am a widower, living in California, writing in response to the woman who signed herself "Second Love." I suspect that her husband doesn't know when he is well-off. He is very fortunate to love and be loved by a second wife. Not all men are so blessed. He should remove all the pictures of his former wife, except possibly one group picture of the family.

Abby, after my wife of 45 years died, I realized that I could never create new memories with her again. When I remarried, I put all my family pictures into a drawer, and I review them periodically.

I cannot afford to let the past interfere with the present. The past has gone, and nothing can change it. I am very fortunate to have loved and been loved by two wonderful women, and I intend to keep it that way. -- DAVID S. EICHER, GLENDALE, CALIF.

DEAR DAVID: Your pragmatism is admirable. I agree there is much to be said about living in the present. However, not everyone reacts in the same manner to loss and grieving.

DEAR ABBY: Recently a reader told you how she used the telephone answering machine to monitor calls for her bedridden husband -- and how he enjoyed listening to his messages, even repeatedly. Such a recording could be a treasured memento of the kind words left by friends and family for their terminally ill loved ones.

I am not ill, but I appreciate hearing the voices of loved ones who call when I am not at home. I, too, play the message back more than once -- for the joy of hearing that voice.

Eventually the answering machine must be cleared, but before I clear it, I often put my cassette tape recorder beside the answering machine and record the messages on tape. Then, if I wish, I can hear them again -- today, tomorrow or any time I need a lift. -- MS. HAZEL DANIELSON, SHORELINE, WASH.

DEAR HAZEL: What a clever idea! I'm passing it along.

Good advice for everyone -- teens to seniors -- is in "The Anger in All of Us and How to Deal With It." To order, send a business-sized, self-addressed envelope, plus check or money order for $3.95 ($4.50 in Canada) to: Dear Abby, Anger Booklet, P.O. Box 447, Mount Morris, Ill. 61054-0447. (Postage is included.)