The title comes from Water for Elephants, the book by Sara Gruen, the full quote being "With a secret like that, at some point the secret itself becomes irrelevant. The fact that you kept it does not."
We were watching Homeland, and there are a few spoilers ahead so be warned if you haven't watched the second season (and we are waiting on the DVD of Season 3 so no spoilers for us please!!). We get to the bit where the wife discovers he's converted and is praying in the garage. She gets extremely angry and upset, and clearly feeling betrayed that the daughter knew and she didn't. At which point, my husband says 'She's more upset about this than the affair'. He was right, she was. It took me a few moments pondering but I could see why. She says something along the lines of 'You lied to me every time you came in here'.
His keeping this secret while he thought he wasn't lying to her, it meant that he was basically someone she didn't know at all. It meant everything in the relationship they had, that she thought she knew, evaporated because either it was false, or she felt doubt about whether it was true at all. Everything became tainted. Not to mention that the daughter was clearly more trusted and a more important person to him. He may not have intended that, but basically, his actions meant the wife, and her feelings, mattered the least to him in the equation. (Though I still would have been more angry about the affair - but that's another post).
I wanted to explore this further, so a bit of googling came up with plenty of articles. There were ones of the obvious lying about friendships with women (and affairs) but there were plenty about lying about how you spend money, how much money you have and where you spend your time (non-sexual). All these things, that seem small, were equally damaging to the relationship because they brought doubt into the mind of the other person.
This article by Sharon Queano, was particularly good and summed up the issue exactly "Did your little white lie do any damage to the integral structure of your marriage?...most definitely if she discovers the truth. Little white lies in a marriage can blur the lines between respect, honesty, and valuing each other’s opinion’s, thoughts, and feelings.... lying can easily destroy the fragile balance of trust the two of you have. Lying can cause doubt, serious doubt, which can erode the structure of the relationship. If it gets bad enough, in fact, your relationship becomes little more than a guessing game, even during those very special heart to heart talks" Taking out the religious aspect of the scenario in Homeland (though that is definitely part of it), I think this is exactly why their whole marriage crumbles shortly after that.
Homeland is an extreme case, as he's keeping many, many secrets, but it is a great case study for a couple not sharing their lives and growing further and further apart. If someone in a couple is deliberately withholding information "an unhealthy distance occurs within the relationship" as pointed out by Shannon Philpott in her article on the subject. You feel shut out, and you can feel the distance, and ultimately, there is that feeling that you don't actually know this person at all. It doesn't have to be the big one, an affair, it can be the examples above or struggling with PND or depression or choosing to spend time with friends instead of being where you said you were or anything at all really.
If your need to do something that you think your spouse will disapprove of, don't keep it a secret. Discuss it. It is better to have the argument before hand than argue later and bring betrayal into the already difficult situation. I'm not saying you have to do everything to please your partner, and not do things they don't approve of. I'm saying you need to let them know you're doing it in advance, and why.
As we often tell the kids, if it needs to be kept secret, it's probably not good for you - think drugs, alcohol, abuse and so on. In this case, if it needs to be kept secret, it's probably not good for the relationship.
Disclaimer: I am not a psychologist. I am not an expert in anything. If I was on Dr Phil, I'd be a guest not an expert dishing out advice (like you needed me to tell you that! Ha!). So this is just my opinion and something I was interested in. I was taken with the point my husband made about a tv show, and I thought I could write an article and sell it to a weekend mag. I, of course, lost momentum and dumped the idea here instead. If you are having any troubles along these lines, see a counsellor or professional.