Can they last. Absolutely.
Are they happy. Who knows. Many will double down and say they are so much happier, they have no regrets and it was all meant to be. Others have fucked their lives and relationships up so badly because of the affair it's what they have left to hold on to.
Irrelevant of the damage they caused to others including potentially their own kids. I find it fascinating that people who ended up fucking their relationships with their first kids go on and have a new family can say it was worth it.
It does however underpin what all cheaters have to have, so they have the ability to cheat. An off the scale level of selfishness, and ability to emotionally compartmentalise.
Once you have crossed the line to cheat, it can easily happen again. Bored? Sexually frustrated? Feeling the strain and boredom of day to life. Someone gives your the butterfly feeling? You already have the experience of lying, gaslighting your partner, you experienced the going home and facing them as if nothing has happened. So now it's so much easier to do again. So just like when you take your cheating partner back it never really goes away that you can believe they won't do it again, I don't believe cheaters who do stay together also don't have that small voice in the back of their head as much as they deny it. Because admitting it would give a glimpse of insecurity because of how the relationship started which would counter the whole "We fell in love, we couldn't help it. It's because we are each other's forever person"
Cheaters like to rely on the "life isn't black and white" line because it provides an avenue to alivate their guilt and publicly seek sympathy and empathy for the most challenging of circumstances they find themselves in. But that's just it. It was all choice, no one held a gun to their head, it wasn't a life or death scenario. It was their need to prioritise their feeling good about themselves over the harm they caused to someone else.
The same way people say Karma will get them in return. Which also isn't true and is something that people hold onto to hope they get payback for the harm they did.
But really the most important thing out of affairs isn't what happens to the two people who created the nuclear bomb, it's what happens the people betrayed.
And as difficult as it is, the sooner they put all of the effort they can into healing from the damage done and focus on living their life the better chance their is they will be able to have a life that isn't forever fucked because of two selfish people. The aim is complete indifference.