Dear Margo: My problem is my live-in fiance of two years had a five-month affair with a client. I threw him out, and he ended it. I have talked to the woman he was seeing and know that he did walk out on her (plus all the seedy details).

He went into therapy on his own; we also went as a couple. He swears I am the woman of his dreams and understands now that he doesn't want to grow old without me. You know all the lines: He was confused, I was distant, she paid attention to him.

I think at present he is being honest. I understand people make mistakes and do things they regret, but I can't seem to forgive him. Do you think people can truly get past such a betrayal and be happy again, or is the trust broken forever?

A good friend advised me never to fully trust anyone. I was happily married for over 20 years to my late husband and fully trusted him. I always swore I would dump a cheater, but here I am in a relationship with one.

So do you think "Once a cheat, always a cheat" is true, or can trust and forgiveness be genuine? — Alicia

Dear Al: Different people have different thresholds for forgiveness. If you understand, as you write, that people do things they regret, and you have feelings for this man, you could probably work through it. I know of couples who have done it, and the hurt does fade.

"Once a cheat, always a cheat" is often the case, but stepping out can also be a one-time thing. As for your friend who said never trust anyone, your own first marriage is proof that she is wrong. I think time will help you come to a decision. — Margo, patiently

WHEN TO TELL THE PAINFUL TRUTH

Dear Margo: I have filed for divorce after 22 years of marriage. During the last 10 years, my husband has been largely impotent, always with some excuse.

Seven years ago, I found that he was writing to a man, but he said it wasn't sexual — although it appeared that way to me when I read the letter.

This past October he posted a profile online saying he was 30 (he's 53), living in another state, etc. The site was a gay fetish website.

I intercepted an e-mail where he was planning to meet a man in another city. They had exchanged photos, and my husband thought the 30-year-old man was "hot." After I confronted him, I told him the marriage was over — this after years of therapy.

My question: Is it appropriate for me to inform his family, who do not know what he is doing, and are filling my two teen boys' heads with lies? I have been advised not to tell my sons, 15 and 17, as they are developing their own sexual identity.

My husband has also told the boys that I haven't "given him enough time to change." The boys are angry with me, but they don't know the truth. — Black Hat in the Midwest

Dear Black: In addition to your own pain and unhappiness, your about-to-be ex is not exactly on cloud nine. This is a man who's not what anyone would call mentally healthy and has been pretending for years ... pretending he's heterosexual, and now pretending he's 30.

As for what he's telling your sons, there's not enough time in the world for him "to change." (And if they do not know about his sexual difficulties, I wonder what it is that he's telling them he hasn't had enough time to change?)

I think it is all right to tell the young men the facts, if only because your husband's family is dealing in untruths to undermine you with your children. And you cannot interfere with their sexual development by giving them truthful information. Their instincts are pre-wired, my dear. — Margo, factually

Dear Margo is written by Margo Howard, Ann Landers' daughter. All letters must be sent via the online form at www.creators.com/dearmargo. Due to a high volume of e-mail, not all letters will be answered.