It's really tricky, because whilst an affair can often end up being public knowledge, what isn't, is what went on behind closed doors for years first, within that marriage.
For example, let's say DH starts becoming mean to me. Maybe starts to become verbally abusive. But we've been together 5 years, and it's new behaviour, and I still love him. He continues, and I become unhappy, but can't leave as I have nowhere to go, financially dependent on him, don't want to break up the children's family home, don't want the humiliation of a failed marriage, all sorts that make it not just a case of "duh, LTB." To the outside world, I smile.
He continues, and my self esteem is affected. I want to leave, I can't see how, I start to make plans for when the children start school. He's really unkind and I'm often in tears.
If I then meet someone, who shows me love and kindness, and offers me a way to leave, into a new and happy relationship, then am I really the devil? On paper, I would be a cheat. The reality is, I stayed for all the wrong reasons with someone who wasn't right for me. I tolerated it as long as I could when I didn't have the means or opportunity of happiness anywhere else, but as soon as I did, I got out of there.
For my husband to then bitterly call him the OM as if he were some deviant that stole his wife, well, it's just not right. And to still be doing that 10 years later?
Each case is different. There will be the stereotypical "cheating bastard" there will be those who were never that suited anyway, there will be those who are just complete arseholes to live with, and the fact that partner cheated is not why the relationship failed. It's how it ended, and sometimes people do stay with complete arseholes, much longer than they should, usually guilt, or for the children, and it's only when someone shows them the physical path out or reminds them that happiness does exist that they manage to break away.
Each person knows what really happened in their individual case, irrespective of what they let the outside world see.