I am a teacher, and one of my students brought a very nice gift for me, leaving it in the school's office.

I never did get it - it was gone the next day. Since I work part-time (only mornings), I did not know about it until the child asked me if I liked her gift. Other teachers confirmed that a gift was brought for each of this child's teachers.Should a thank-you note be sent for a gift that was not received?

GENTLE READER - What is the assumption from which you are asking this question?

That one expresses gratitude at a gain in possessions, rather than for the generosity bestowed?

That you can ignore the kindness of a child if its object was thwarted by dishonest adults?

Miss Manners suggests that you not try to teach etiquette, even part-time. And that you write a letter this minute, telling the child how much you appreciate her thoughtfulness, referring to the theft only by saying that a misunderstanding prevented you from realizing earlier that she had sent you a present.

DEAR MISS MANNERS - After several months of courtship, my boyfriend and I, both in our early 30s and well-established in professional careers, experienced a birth-control failure, and I became pregnant. We were not living together.

In our pre-intimacy conversations, we both expressed a desire to have a committed relationship and "settle down." Also at that time I let him know that if a pregnancy occurred, I would not seek an abortion.

When he learned of the pregnancy, he responded that he was not ready for marriage or a child. Now that I am in my third month, he is all but completely absent from my life. The important details of providing and caring for the child are secure, as I have a good income and own a home.

Even though I have a supportive family and more than my share of wonderful friends, I cannot help but feel embarrassed and shamed by this turn of events. I need to be comfortable about fielding the expected questions regarding marital status and the surrounding details, so that I may remain cheerful and hold my head high through the pregnancy. I feel no obligation to provide these details, but what can I say to colleagues and clients that is firm, yet not unfriendly?

GENTLE READER - Miss Manners presumes you are asking about questions that are well-meant and within the bounds of what business people can properly say to one another, but she can't think of many.

"Are you married?" is not one of them. Perhaps "I suppose your husband is thrilled?" would be. But not what you gently call "surrounding details."

In any case, you should not be engaging in personal discussions on the job. This applies to married expectant mothers as well as unmarried. Not only is it unprofessional but it encourages nosiness, the extent of which nowadays would astound you.

The proper reply for you to make to any such question is "The child's father and I are separated." Say it in a firm enough voice to indicate that the matter is not open for examination. And should anyone be so audacious as to ask why, the answer is "Because we are living apart."

DEAR MISS MANNERS - I rent a large home, in which I have two roommates. My 6-year-old son is here four days a week.

Upon taking in my second roommate, I unknowingly acquired a third. It turned out, after the first three months, that my second roommate opened our home to a friend of hers whom neither I nor roommate number one knew. She came and went as she pleased, staying one month.

During that month, the second roommate justified her friend's presence by saying that she wasn't there much herself. After this person left, another of her friends began staying - at first just a few nights a week, but then full time.

Originally we agreed to split the household bills three ways. When I confronted the roommate about splitting the bills four ways if the friend was going to continue staying, her response was that her friend's parents were paying rent and bills for her at another residence (in another city), so she didn't know if the friend would want to continue staying if she had to pay bills.

They both stayed another month, then moved out. So bills came, and they then informed me that the friend wasn't paying her share. They brought up issues of how many times they turned on the heat, how they took short showers, and - imagine this! - the fact that my son bathed and used electricity.

Am I being petty? Does common courtesy exist? Do nice guys finish last?

GENTLE READER - Miss Manners is afraid that even nice guys cannot depend on niceness to settle such issues as when a house guest becomes a roommate.

Common courtesy is in short supply and not evident in the way your former roommate is now behaving. But common courtesy cannot negotiate financial responsibilities in a contractual arrangement. To avoid finishing last, one takes up the matter first.

1991, United Feature Syndicate, Inc.