DEAR ABBY: I am a 13-year-old girl. I have a sister who is 19 and has been married for a year. One day last week, her husband told me how beautiful he thought I was and how much I had developed lately.

Later he gave me a ride to my girlfriend's house to pick up my bike. On the way back it was quite dark. All of a sudden he stopped the truck and asked me for a hug. I thought, "What the heck, he did me a favor to drive me to pick up my bike, so it's no big deal to give him a hug." Well, it was a real long hug, and he wouldn't let me go. Then he asked me for a kiss, and I said, "No way ... no, NO!" He knew I really meant it, so he let me go. Neither one of us said a word until he dropped me off at my house.

I really feel uncomfortable around him now. I can't tell my sister or anyone else because my sister really loves him and I couldn't live with myself if I made trouble in her marriage.

If you want to print this to warn other teens who may run into a problem like this, please don't use my name. -- THE KID SISTER

DEAR SISTER: You were very, very wise. Thanks for sharing your experience as a warning to other young girls who could be taken advantage of by a relative or close friend.

DEAR ABBY: We got a good chuckle out of "Very Disappointed" who spent her wedding night on a fold-out couch in a fancy hotel. Your advice to double-check reservations was very good, but it doesn't always work. Here's our story:

We had arranged the "honeymoon package" at the then brand-new Hilton in Erie, Pa. We arrived late on our wedding night and were warmly welcomed at the front desk. When we got to our room, we found the promised bottle of champagne and a very lovely large room -- but no bed! It seems one of the couches was a fold-out bed with one pillow and a set of sheets (no blanket)! When we telephoned downstairs, we were informed that the hotel was full and "housekeeping" was closed for the night, so we were out of luck.

When we folded out the bed and sat on it -- it collapsed!

But what the heck? We've had many laughs over that story through the years. We've often said that a couple without a sense of humor could have broken up over such a series of incidents. Let's hope the honeymoon couple in that classy Dallas hotel survived their disappointment.

As for us, 13 years later, we're ... STILL LAUGHING IN GRASS VALLEY, CALIF.

CONFIDENTIAL TO V.N.: You know you're getting old when a lady you've never met before is seated next to you at a dinner party and she asks which is your good ear.

Want your phone to ring? Get Abby's booklet, "How to Be Popular" -- for people of all ages. To order, send a long, business-size, self-addressed envelope, plus check or money order for $3.95 ($4.50 in Canada) to: Dear Abby, Popularity Booklet, P.O. Box 447, Mount Morris, Ill. 61054. (Postage is included.)

DEAR ABBY: I am desperate, so I will tell you my problem from the beginning. I am a 35-year-old mother of three. I divorced my husband twice for the same reason. Both times I caught him with another woman. (The same woman, and she was my best friend.)

Now I have a guy I think the world of. I love him like I have never loved anybody in my entire life. I can't stand being away from him. We have everything in common. He keeps telling me how much he loves me, and I know he isn't lying. He treats me like a queen. There is only one problem. He's living with another woman. He says he doesn't love her, and I believe him. He's too kind and decent to tell her he's in love with another woman. He says if she knew, she might even kill herself.

He doesn't want me dating anyone else, but he goes home to her every night and I'm alone.

I'm tired of hiding, but I'm afraid if I force him to make a choice, it won't be me. What should I do? -- A WOMAN IN LOVE

DEAR WOMAN: Brace yourself for some unpleasant news. The guy you are in love with has already made his choice, and it's not you.

Quit being available whenever he wants you. And quit hiding. The man is living with another woman, and he's cheating on HER to be with you. Please wise up and smell the skunk cabbage. This man is not worthy of your love.

DEAR ABBY: Tonight, while shopping at a large department store, I witnessed a man pull his son's hair and then he kept punching him very hard on his back and shoulders in an effort to make the boy obey.

The boy looked to be about 7 or 8 years old. The poor kid sat on the floor and cried silently while his father delivered these cruel blows with hate in his eyes. I stood no more than 3 feet away throughout this episode, searching for the right words to demand that he stop hurting the boy, but I feared that if I said anything, the man would be angered and embarrassed and would take his anger out on the child later at home.

Please address this issue, Abby. Tell your readers how to handle such situations. -- FEELING GUILTY FOR MY SILENCE

DEAR FEELING GUILTY: The scene you witnessed involved a man out of control. You could have very gently and quietly attempted to calm the father by saying, "I know exactly how you feel. Sometimes taking a child that age shopping is more than we can handle." And without being judgmental, in a soft and sympathetic tone, you would have intervened and brought an out-of-control man back to reality.

This sometimes takes more courage than most people have in today's "mind-your-own-business" society, but to do nothing while witnessing child abuse is indefensible.

Readers: There is now a toll-free National Child Abuse Hotline for adults to call when they feel that they are losing control. Dial 1-800-422-4453.

Most teen-agers do not know the facts about drugs, AIDS and how to prevent unwanted pregnancy. It's all in Abby's updated, expanded booklet, "What Every Teen Should Know." To order, send a business-size, 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. (Postage is included.)

DEAR ABBY: I am desperate, so I will tell you my problem from the beginning. I am a 35-year-old mother of three. I divorced my husband twice for the same reason. Both times I caught him with another woman. (The same woman, and she was my best friend.)

Now I have a guy I think the world of. I love him like I have never loved anybody in my entire life. I can't stand being away from him. We have everything in common. He keeps telling me how much he loves me, and I know he isn't lying. He treats me like a queen. There is only one problem. He's living with another woman. He says he doesn't love her, and I believe him. He's too kind and decent to tell her he's in love with another woman. He says if she knew, she might even kill herself.

He doesn't want me dating anyone else, but he goes home to her every night and I'm alone.

I'm tired of hiding, but I'm afraid if I force him to make a choice, it won't be me. What should I do? -- A WOMAN IN LOVE

DEAR WOMAN: Brace yourself for some unpleasant news. The guy you are in love with has already made his choice, and it's not you.

Quit being available whenever he wants you. And quit hiding. The man is living with another woman, and he's cheating on HER to be with you. Please wise up and smell the skunk cabbage. This man is not worthy of your love.

DEAR ABBY: Tonight, while shopping at a large department store, I witnessed a man pull his son's hair and then he kept punching him very hard on his back and shoulders in an effort to make the boy obey.

The boy looked to be about 7 or 8 years old. The poor kid sat on the floor and cried silently while his father delivered these cruel blows with hate in his eyes. I stood no more than 3 feet away throughout this episode, searching for the right words to demand that he stop hurting the boy, but I feared that if I said anything, the man would be angered and embarrassed and would take his anger out on the child later at home.

Please address this issue, Abby. Tell your readers how to handle such situations. -- FEELING GUILTY FOR MY SILENCE

DEAR FEELING GUILTY: The scene you witnessed involved a man out of control. You could have very gently and quietly attempted to calm the father by saying, "I know exactly how you feel. Sometimes taking a child that age shopping is more than we can handle." And without being judgmental, in a soft and sympathetic tone, you would have intervened and brought an out-of-control man back to reality.

This sometimes takes more courage than most people have in today's "mind-your-own-business" society, but to do nothing while witnessing child abuse is indefensible.

Readers: There is now a toll-free National Child Abuse Hotline for adults to call when they feel that they are losing control. Dial 1-800-422-4453.

Most teen-agers do not know the facts about drugs, AIDS and how to prevent unwanted pregnancy. It's all in Abby's updated, expanded booklet, "What Every Teen Should Know." To order, send a business-size, 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. (Postage is included.)