I know all about the "very strong emotional shock" felt by Valérie Trierweiler, hospitalised after discovering her partner, the French president, François Hollande, has been allegedly having an affair. Four years ago, I discovered that my husband of 15 years was having an affair. It was the biggest blow I've ever had in my adult life; but it's interesting she compares it to being hit by a high-speed train, because no one would survive that. And what I've discovered – and I hope Trierweiler discovers this too – is that while the immediate upset is terrible to live through, its aftermath can make you stronger; and though I couldn't say it turned my relationship around, it did give my husband and me a level of honesty that I think many couples don't have.

My moment of truth came out of nowhere. A relaxed, sunny afternoon with my children; an innocent misunderstanding about where to find some information my husband had left me; and wham! There it was in my hand, a message of love she had sent him. And it was love, quite clearly; that was indisputable. This wasn't a fling or a one-off or a later-regretted we-had-too-much-to-drink-and-ended-up-in-bed-together. This was a lover, in every sense of the word. In the moment I understood that, the ground beneath my feet fell away; and four years on, I know that it never will, and never can, be entirely solid underfoot again.What happened to me next was exactly what happened to Valérie Trierweiler last week. I felt utterly undermined; insecure in a way I had never felt insecure before. Everything we had built up in our life, the investment we had put into our family, the plans we had for our future, the entire existence we had together, went in an instant from being the solid structure around me to a house of cards that might be about to tumble down, and that I had no idea whether I would be able to rebuild it alone. Worse – and this really was the worst of all – I felt like an outsider in my own marriage. It was clear that "she" was the person with whom my husband was actually having an intimate relationship. I was the appendage, the sideline; maybe I was even the joke. They, my husband and his lover, knew everything that was going on in my marriage; they had the 360-degree view. I only had partial vision; no wonder it was so difficult to imagine the road ahead.It was devastating but, of course, life had to go on. Everyone knows about Hollande's alleged infidelity, and only three of us knew about my husband's; but I really don't know which is worse. Of course, Trierweiler is having to deal with the publicness of betrayal, and that is desperately humiliating; but I had to deal with the privateness of it (as most people who go through this have to do) and it was desperately lonely. One thing you quickly grasp, when you are in this situation, is that you're going to have to be very careful about who you tell, especially if there's any hope that you will continue in your marriage. It's not only that your friends will turn against your partner, it's also that you won't want them to have turned against him once you start trying to repair the relationship. And so you rely, very heavily, on a trusted few. To the rest of the world – and, crucially, to your children – you have to be as jolly as ever. I remember dragging myself out of bed in the morning and struggling to stay cheery as I made breakfast and waved them off to school, before coming home and collapsing in a heap on the hallway floor. My husband, meanwhile, was at his office, where everything was as it always was, and he could ignore our domestic meltdown. I, who had no job outside the home, was surrounded, all day long, by the very fabric his actions had threatened, and I remember how panicky it made me feel. I don't know that I was quite ready to be hospitalised, but I can understand how it could make someone feel bad enough to need to be.Four years on, though, I'm glad I went through that time. Our marriage was what it was, and it is what it is; and finding out about my husband's affair meant that I, too, could see our relationship in 360 degrees. He eventually ended the affair, and he and I stayed together; though things can never be the same, we have created a new normal. What I'm glad about is that there are (probably) no secrets, and that we've both had to acknowledge the things that weren't working in our relationship. Solving them isn't proving to be easy; but finding out about the affair at least meant I could begin to get to grips with the extent of the problems.• Judith Laine is writing under a pseudonym(theguardian.com)ANN.Az