Long term consequences of lies/omissions & RJ
On TAM, the popular way of looking at something that was lied about or hidden, and discovered many (decades?) later, is to claim the issue is retroactive jealousy and largely a problem with the person who (finally) discovered it. Beyond whether that is actually the case (retroactive jealousy) and not a revelation of the root of some issues in the marriage, it also implies that it's better to keep the secret if you believe you can keep it a secret.
That gives power to the decision to lie in the first place. And here's the thing about many lies. Once created, that lie becomes an increasingly-bigger problem, over time, if or when the truth is revealed. So much may have been built upon that lie that the risk of an extremely-negative response becomes the overwhelming driving force to keep the lie going.
Initially, that lie or omission might have felt like what someone needed to keep someone interested in them. It might be something that, if revealed, might frighten the other person away, or at least put them in a negative light. I'm not suggesting that everyone should be an open book at every point in a relationship, but there is a HUGE difference between not bringing something up (because it might be none of their business after all) and not telling the truth, or a reason for not answering (such as, it's my right to have some privacy about my past) when directly asked.
Lies and omissions can create retroactive jealousy that otherwise might not have happened. Even 42 years later. Things that, if discussed early on, would have been no big deal. Things that, because they were outright lied about, created a very different narrative, a different story, about the person you fell in love with. You followed that script and behaved accordingly. You may have changed your own views to better accomodate his or hers. And in some of us, that early story imprinted upon our brains and became the foundation for our lives.
Still easy for many to say look, years have past, you've been generally happy, he/she's been there for you, do you really want to risk throwing it all away by bringing up stuff from ages ago? But using the story theme, stories have beginnings, middles and ends. You don't start in the middle. Sometimes an effective way to frame a story is to actually reveal the end and then show what lead up to it. The beginning is always important, at least to those who believe in stories and narratives that describe a journey and not a series of unpredictable events.
My own personal experience leads me to believe that we routinely discredit the damage that can be done by lies and omissions many, many decades past. We crucify mercilessly for those in the present or near present or even 10 years ago. But unless it's adultery, the ramifications of something discovered is supposed to somehow be softened greatly with the passage of time. For many, that's not true, and those lies and omissions may very well be tied to creating a nearly PTSD-like issue for the person holding back, because that person may be wracked by guilt, at least initially, and over time harden themself into believing that lying (about other things) is the right thing to do, because it helps them to rationalize the earlier decision(s). It can poison the relationship in insidious ways.