Yes I did mean if it was a true one-off. I can understand the needing to confess part - I think that drives a lot of us to confess these things. I have never cheated in a relationship but I just know even if there is a small incident where I have screwed up I end up having to confess for my own sanity and that is the point I was trying to make. It is often for the benefit of the confessor's conscience rather than as an act of duty to protect the other person.
There is no easy answer though. On the one hand one could use the argument that for a definite one-off indiscretion it is best for both people to forget about it. On the other it could be a sign that something is wrong in the relationship and that it might happen again. I think if the partner who cheated does understand that is wrong and has no intention to do it again then I could understand keeping the secret.
I still feel a bit conflicted about it because I think it is drummed into us from an early age that we should not keep secrets in these situations and that secrets are bad.
Unfortunately life is complex and things are rarely that black or white particularly when it comes to human relationships.
Yes I think when people are younger then you can almost forgive these kind of things more easily because they are still learning and inexperienced. The feelings and the sense of having your life ripped apart is just as intense though.
Great post though and good food for thought and discussion.