I have honestly never really seen or heard of anyone really having a properly happy marriage afterwards, no.
It's very much a compromise - staying in what's now a fundamentally quite painful situation as they've decided on balance that it's better.
For those who continue to conclude that it is better, I'm sure you could say it works, it DOES work in that they have the situation that they'd 'prefer' out of splitting or staying.
But no never properly happy, because - well, you know why. How can you be - the whole idea of marriage is to have that bond with the person who is supposed to have your back - and you realise that they've betrayed you in the worst way you can. To do so for the cheap thrill of a one-night fuck isn't actually better, either.
You stay in an arrangement but it's no longer marriage proper.
There have been many posts I've seen where the poster is vehement in describing how it's actually IMPROVED their communication and sex life and blah blah, mind you.
All with a faintly hysterical trying to convince themselves air.
Just go into it with eyes open and immediately start building a mental life without him and a support system - I think you'd soon go mad if you didn't, as you'll never have trust again.