Adrastea - To be fair, I do believe it is infinitely worse in some situations, although not in others. I believe it would have been infinitely worse in my DM's situation to leave and this is what I was primarily referring to.
To be honest, I think if there are no children involved, both people are young and either one or both are desperately unhappy then they both have a good chance of a new life with someone else and divorce is justified (although not completely morally unambiguous).
But if you're not young and/or there are children involved, then leaving your partner is a whole different kettle of fish. First let's deal with the age thing.
It is far harder to find a life partner in your 60s or 70s than it is in your 20s and 30s and some people who divorce late simply never find someone new (I am 30 and despite years on dating websites have yet to meet ANYONE). I know people will say that they know plenty of people that manage it, but the fact is that plenty of people don't. I know people will also say that having the chance to do so is better than living in a marriage you are content with but in which your partner is cheating, unbeknown to you, but I disagree. If my partner left me when I was approaching old age I would be devastated and absolutely livid, no matter how badly we were getting on. I would far rather he sought some fulfilment elsewhere and respect the most important of the wedding vows, because it's the always part that distinguishes a marriage from a LTR.
And then there are the enormous financial implications. If you divorce young, you have far less to lose and also plenty of time to earn back the money you lost in the divorce process, but if you leave someone when they're 65 or so, they may never recover financially, and their plans for old age can just completely unravel. I do not believe at this stage that it is fair or ok to divorce someone just because you are unhappy. I think leaving, under these circumstance is infinitely worse than having an affair. Marriage isn't just about happiness; it's also a promise and a contract not to do the other person over financially by abandoning them in old age when their chances of recovery are low.
And when it comes to children, I agree that if the marriage is a living hell and the children are obviously suffering it is once again in everyone's best interests to dissolve the marriage. But if the kids aren't unhappy they will suffer enormously from a divorce, not just in the short term but possibly all throughout their lives. They may even be left with the burden of having 2 sets of elderly parents to care for in their old age, as happened to someone I know. Their mother remarried a man without children and their father remarried someone who's kids lived abroad and visited rarely. The result was that all the care and support for both sets of "parents" fell to him. Then there's the issue of your kids growing up in a step family. They haven't chosen this and they may not get on with the person you/your x chooses and the family that comes with the step parent. It's not fair to impose this on them unless they are actually unhappy living with their parents.
And then there are the safety issues too. I have a friend in the police and she says sexual predators often seek out relationships with single parents to give them access to their children and that dating sites have become a gold mine for them. They have all the relevant information (often children's ages etc) and an idea of the parent's personality type and temperament and can pick out the type of person that is an easy target with very little effort involved at all. Even if you're as careful as can be, if you can't control how your x will try to meet new people, this is a risk your children will have to face. (Don't mean to scaremonger as it's not going to happen to every second family but it is a risk). Starting again with kids involved should be an absolute last resort; an affair, in my opinion, the second last resort.
I still stand by what I wrote on the other thread - but I was addressing the situation regarding the children and how they're affected. It sounds like the OP was being treated very badly by her husband, and her dc were suffering distress as a result. If so, I think she needs to get out, I really do and she shouldn't feel guilt for doing so. The kids may very well initially feel relief and be better off overall but (as she acknowledged) they will not emerge completely unscathed.
I suspect my DF would really struggle to find anyone else at this stage. He has multiple health problems and given his social skills issue I can just see him coming home to an empty house every day until his life is over. He has few friends and isn't good at making them. Neither parent would have the same financial security they both worked so hard to give themselves.
My DM on the other hand has everything going for her and I think she would find someone new relatively easily (if not the OM). And while I don't believe we all deserve to be happy at any cost to others, I think we deserve it in certain situations, my DM's is one of them. She has put her heart and soul into her marriage, she really has.
My DF has burried his head in the sad and ignored an issue that has drastically reduced the quality of my DM's life. He has arguably broken his vow to love and protect her by ignoring her sadness. As he has refused to meet her needs (or try to meet them) I think she has the right to seek other means of meeting them. She signed up for a marriage in which both partners do everything in their power to take care of the other. She didn't get what she thought she was getting. I love my DF to bits but I think he does deserve to suffer the consequences of his failing. My DM gave him decades of opportunities to fix something that only he can fix and he hasn't. She did not do this lightly as I think someone implied or suggested. If you cannot or will not attempt to meet someone's needs in the long term it's selfish to say they are not allowed to seek to get their needs met in other ways.
All this said I am incredibly glad my parents are still together. They do have a friendship to some degree and they are a team. They have plenty of good points and they love me and my siblings. I love spending time as a family unit and it would break my heart if they split up.