I drove my daughter to the train station recently, fighting back tears. She is going for only two weeks. She will be home soon. And then she will leave, again.

I know I am lucky. I’m afraid even to say it – the evil eye and all that. Knock on wood. My daughter is going to Mexico, not to Iraq. She is going to a safe place, not a dangerous one. I’m the kind of mother who reads the obituaries every day, about the kids – because that is what they are to me, those who are dying in Iraq – and about the mothers who didn’t want them to go. My heart aches. I get the details of the kids who overdose, drive drunk off the road and don’t get to go on fun trips or study college catalogs. I know I am blessed. I thank God every day. But I still cry on the way home from the train.

In a year, my daughter will go off to college. Already the search is on for the right fit, and it is not, as it was when I applied, limited to schools on the subway line. But it didn’t really matter that I was only two transfers away, when I was my daughter’s age, I left home and never went back.

My daughter goes in a year. Then her brother will follow, in two or three. God willing. Thank God. It is nothing to cry about. But I do.

I remember when my children were little, friends and strangers would look over and tell me to enjoy it, that it would be over in a minute, that they would be gone before I knew it, that the children I was carrying would soon be driving away. I thought I understood, but really I didn’t. When your kids are little, time doesn’t fly. Some nights are so long, with so little sleep and so much frustration, that you can forget you are living the happiest days of your life.

I thought I knew the important things. After all, I was “old” when I had my kids. I had seen fame, found success, learned it was fleeting, experienced its limits. I thought knowing what mattered would somehow make it last.

And then I blinked.

By the time you understand that time is short, it has begun to fly. When I was young I couldn’t wait. Time passed slowly. Now I want to hold on to it, and it rushes past me.

The days my children were born were the happiest days of my life. I remember what it felt like, like it was yesterday. But it wasn’t.

My friends tell me it is different today, that kids don’t leave the way we did, packing up and never coming home. They can’t afford to. They don’t want to. They aren’t as old as we were at their age, aren’t as angry. They have homes to come home to, better than the ones they can make themselves – something I never had. When I went to college, my parents broke up, and that was it. Neither of them had a bed for me, much less a room, in their new places. There was no question of coming home. I didn’t have one.

My friend Pam’s daughter left for school five years ago. Now she works in New York, while her mother keeps her room for her in Oklahoma City. I ask her advice, and she doesn’t really have any. She tells me the truth: that she still gets teary about her daughter being gone.

I know there are some who look forward to the empty nest, to the time for themselves, to the trips they can take and the things they can do. I don’t. My children are not yet gone, but already I look back at the mistakes I have made, the time I have wasted worrying about bills and spills, about moving and money, about the bickering and the messes and all the things that don’t matter, even as time raced by.

I tell myself that when my daughter comes home, I will make each day count, that the time may be short but it can also be rich, that it’s not about how many days before she goes but how we use those days. I try to have faith in the universe, that everything is as it is supposed to be. I hold on to the idea that a little faith is like the salt in the soup, what it needs and what I do. I repeat these things to myself to feel better, but I know something else: I will blink, and she will be packing again. And I will cry all the way home.

Susan Estrich is a syndicated columnist and author.