I agree with the last few posts.
I think that couples should talk about infidelity, rather than sticking their head in the sand in the belief that it could never happen to them. Pre-affair, I believed that I would be more capable of infidelity than my H. Because I also believed that I would never actually do it, I reasoned that it was me who controlled the fidelity in our marriage. I now realise how smug and complacent I was - we can never control what our partners will do, however well we think we know them.
Butterballs is right - infidelity is sadly a part of life and the people practising it are not the devil incarnate - they are often good people in good marriages. I think to understand this, it helps to empathise with temptation. Because I have been tempted myself, I know how difficult it can be to resist someone telling you how wonderful you are all the time. If this happens when we have got high self-esteem and don't need an outside boost or a bit of escapism, it is easier to resist (my case).
If it happens when life is a bit grim and we are feeling unattractive and unappreciated, it is harder (my H's case). My H did turn down several earlier opportunities to be unfaithful (including with OW, when she was 13 years younger and 4 stone lighter!) but when ever these happened, he was in a better place in himself, so it was easier to say "no".
I don't think it helps us understand infidelity if we think of it as evil behaviour conducted by evil people. It is certainly horribly destructive, very painful for all concerned and not to be recommended, but we need to understand that it could happen to any one of us.
It is therefore much healthier to discuss the possibility of infidelity openly together - how to protect the marriage from it and devise strategies together to cope with inevitable temptations. It's also a good idea to identify each other's "weak points". It's a mistake though to concentrate these efforts on the errant spouse only - or more unusually, as in VCAU's case, the betrayed spouse. Both marriage partners need to work on affair-proofing the future marriage and this can only be achieved by being honest about the nature of temptation.
I agree that throwing a relationship away because of infidelity is often regretted by people after the event. I had to tell myself in the early days that my wounded pride and ego should have no part in affecting our children's lives and futures. However, I also know I could never have stayed with my H solely for the children's sake either. We have both worked very hard to create a new marriage that is more honest and I often think, more "grown up" in that we don't pretend any more that dreadful things can never happen to us. Like HW, I do sometimes regret the loss of child-like innocence, but not so much nowadays. In a way, that innocence led to complacency and disbelief and so I have grown to dislike it.
Like Butterballs, I dislike gender distinctions, but I do think men have traditionally been more pragmatic about infidelity. They do not necessarily see this as a forewarning that the primary relationship must be doomed and are able to separate more easily. Whereas I think a lot of women delude themselves that they must be terribly unhappy to be even considering another man. I am sure this is why my H's OW must have been baffled (and disbelieving) when my H told her he loved me and his marriage was happy.
I am seeing now though that unfortunately, men are becoming more female in their thinking and are leaving perfectly good marriages - and women are using "fuck buddles" to prop up their marriages. It is still destructive behaviour though, whoever is doing it.
Better I think to acknowledge the risk, discuss how to prevent it and have an honest dialogue about temptation, weak-spots, secrets, lies and moments when we could be more vulnerable than others.