Last week, I was reminded once again of why it is such a blessing to have a close group of long-time friends. In addition to other considerable joys, they provide a collective memory bank — and they keep us honest.

Case in point: When I answered the Question of the Day, “What is the biggest lie you have ever believed?,” I rather smugly said I never really believed the big lies. I was thinking of the sort of big lies your parents tell to “protect” you when you are younger, or of the lies politicians tell and often believe themselves. And then I got an e-mail from my friend M.T. that asked: “What about that dude who said he’d gone to Vietnam?”

The dude, who I’ll refer to as “Andrew,” was a man I was involved with for about two years when I was in college in Washington, D.C. He was older than I by about eight or nine years and had some kind of amorphous political job, though some exciting deal was always looming on the ever-shifting horizon. This was a period in my life when my self-esteem was not exactly at an all-time high; we shared a tiny apartment and I managed to ignore all signs that he was crazy.

Not only did he tell me — and all my friends — that he had gone to Vietnam, he put on a hell of a convincing show. He had bumpy scars on one of his shins and every once in awhile, tiny bits of metal would work their way out, and he’d explain that they were shrapnel. In the middle of the night, he’d wake up sobbing from a “flashback” nightmare. The scenes he described were so graphic and so horrific — one involved the brutal sexual torture of a South Vietnamese girl by the Viet Cong that I can still visualize — they don’t warrant repeating.

One night, he left the house for some cigarettes and didn’t come back until the following morning. He told me he’d run into the sister of a guy whose skull he’d held together as he lay dying. She’d been upset and needed to talk to him, he said, and he couldn’t just leave her like that. (Much later, my busy-body landlord told me he’d often seen him ducking into the neighborhood strip joint.)

An increasing number of episodes like the latter prompted a conversation with his brother, who was also concerned by his increasingly erratic behavior. “Maybe it’s the Vietnam thing,” I said. To which the brother replied, “What Vietnam thing?” “Well, you know,” I said, “his experiences in Vietnam — I think he’s having trouble with them.” When he gave me the news that Andrew had never been to Vietnam, I actually argued with the poor man, presenting all the evidence on Andrew’s behalf. When I finally realized that he was telling me the truth … I don’t think I’d ever felt such enormous relief.

It was Andrew who was crazy, not me. He wasn’t acting like a bastard because I deserved it; he was just deeply disturbed.

In thinking about this experience, I think I finally have a bead on what motivated Silda Spitzer’s seemingly loyal behavior in the wake of a far bigger bombshell. First, there is shock because pretty much everything that has defined your relationship turns out to be a lie. But when the pathology is so deep and the demons so seemingly numerous, there is an immediate-and welcome-distance that occurs. Not a distance like “I never want to see the S.O.B. again,” but a calm clear-eyed ability to see that these are compulsions that don’t have anything to do with you. You don’t get angry as much as say, “Ah, I get it now.” Or at least that’s what I did.

I didn’t even kick him out-at first. I told him what I knew, and after he’d briefly tried to convince me that it wasn’t true, he agreed to get help. Getting him to see a shrink was the only immediate and sensible thing I knew to do. In a matter of hours or even days, I wasn’t ready to decide what to do with myself (make him move, move myself), but it was clear that he needed to do something.

After the Spitzer debacle, I called several therapists for a piece I was thinking of doing in Vogue on why women like Silda Spitzer literally stand by their men after such awful transgressions are revealed. Dr. Brenda Shoshanna, author of Save Your Relationship, cited the shock factor. “It takes a long time for something like this to sink in,” Shoshanna says. “To move very quickly out of her typical mode of behavior would be unthinkable. Showing up, standing there-that is what’s expected of her.”

Mira Kirshenbaum, a Boston-based couples therapist and author of the upcoming “When Good People Have Affairs,” told me pretty much the same thing. “People almost always act out of consistency,” she told me. “In times of crisis, the way they have been is the way they will be.” Right, I was the fixer in my family. I’d been brought up to think it was wrong NOT to try to control everything. So I figured I could control this particular situation and fix Andrew.

Fortunately for me, Andrew wasn’t all that interested in being fixed. He missed more shrink appointments than he made and when he disappeared for two days — with my car — I was more than ready to kick him out. By this time a few months had gone by. Unlike the Spitzer situation, there were no kids and no joint property. Silda may decide to try to save her marriage (which all the shrinks I talked to said was possible but would require a “team” of therapists) or she may decide to put her life back together without him. Either way, I can’t imagine it is a decision she has even yet made. I was 20 years old when I found out, privately, that somebody I had been with for two years was a nut. Silda’s marriage has lasted longer than I’d been alive at that point.

Also, like with all political couples, a pact of sorts had been made that most folks don’t have to make. “We make a deal with the devil when we enter public life,” says Jeff Gardere, a Manhattan-based clinical psychologist. “We know that whatever happens — good, bad, or ugly — it will play out on a public stage.” So it is, he says, that standing by one’s husband “is part of the job description. These women are not being forced on stage at gunpoint. They know that it’s part of the paces of public life. It was part of the deal they made to be first lady of a city, or a state, or a nation.”

Interestingly, though, Gardere does not see the compliance with that bargain as necessarily demeaning. Rather, he says, it can be empowering — and for all the legions of female bloggers who found Spitzer’s support of her husband “nauseating,” there were a great many who found her a compelling, even admirable figure. “These women are showing the world that there is no shame in their game,” Gardere says. “They may be in shock, but they are also demonstrating a tremendous amount of underlying strength. While their husbands have clearly disgraced themselves, their families and their office, they are saying ‘I’m going to show you who I am as a person, that my standards remain at the highest levels as a wife and as a partner.”

Gardere’s “no-shame-in-my-game” point goes to the clear-eyed distance that I felt after first getting the news from Andrew’s brother. Okay, this guy has some big-time issues, but I am going to be cool, I am going to try to help him, I will not throw stuff or make a scene. It wasn’t what the situation warranted. This was a lie that was bigger than me and it was far easier to deal with than the legions of little lies and disappearing acts.

So I am grateful to my old and dear friend M.T. Not only did she remind me of a big lie I bought hook, line and sinker, she served me a dose of humility. From now on I won’t be quite so glib with my answers, not just about “big lies” believed, but about whether or not women like Spitzer should leave their husbands. It’s complicated stuff and who the heck am I to judge?