Yes there are choices but by the time you realise a choice has to be made it becomes a very, very painful choice to make and this is where the problem lies imo. Someone said you slip into these things, slowly, slowly and it's true. Nobody wakes up one day and just decides to begin something inappropriate with somebody. And yes sometimes they do happen because of distant/critical/whatever Husbands or wives.
You're down, you're not happy and then in the most random chance circumstances you meet someone who blows your socks off. It's wrong, you can't eat, you don't sleep and everything you knew just seems different. It can be an overpoweringly strong pull towards this other person who is treating you the way you should be getting treated at home but you're not and you've concluded you just don't have the right words to make your spouse listen up because this shit is a really slippery slope now but nothing physical has happened and I can tell myself it's just friendship...
Then you've slipped that bit further and you pine for them (genuine chemical, primal reactions that you really can't control and more to the point, don't want to because you're in love and you feel amazing and that is the kind of high it's very difficult to come down from). I'll just see him one last time and walk away. You're not actually being a selfish boot, you find the thought of people hurting because of you and your actions physically painful to contemplate - so you don't.
You bury your head in the sand of knowing it will come out and it will hurt everyone involved but just a little bit more of the drug I've become so addicted to and then I'll deal with it.
In the end I walked away from the affair and concentrated on my family (yes, I did tell my husband and in all honestly I'm not entirely sure it was the right thing to do) because I do love my husband, I'd put my life on the line for him. I've done a bad, bad thing that I feel has totally tainted me as a person. But I'm really not a bad person.
Walking away is so much easier said than done. Maybe we could have been happy, maybe I threw away that one chance of passionate love but I fucked up, tough shit on me if it hurts till the day I die but ultimately I must have loved my husband more. Or maybe I did what society expected me to do. Either way I do now have a good marriage because ironically it made me husband wake up to how miserable he'd been making me for so long. But I'll bet my house on it that there are loads of families/people out there who will have been in this situation. An untold lie or omission of a few truths does not mean a marriage will always go down the pan. I guarantee people have their secrets and continue to live a perfectly normal life, their blip way behind them and a marriage that survived. There are nowhere near as many foregone conclusions that people would have you believe.