On a writers' forum that I participate in, the question was asked about how to motivate a character to stick with his first love once he becomes famous and successful, and suddenly finds himself surrounded by willing women. I found this something of an odd question. True, in real life, many men abandon their first wives once success gives them more opportunities, but I never would have thought it difficult to figure out a motivation to stay.
I've been married for two years, which is not much in the scheme of things, but I can say with some certainty that the reasons I love my wife don't go away the moment another opportunity comes along. So often what we love about someone is in the small things, the quiet moments when nothing is demanded and we can just be together, and it doesn't matter how rich one is or how successful someone's become. How much do they trust one another? How willing are they to share their secret fears and dreams and doubts without worrying about being judged? What inside jokes do they share? How well do they know each other's failures and weaknesses, and accept one another anyway? What do they talk about when they lie in bed together at night, just talking? How do they argue and make-up, and either compromise or agree to disagree? How do they show support for each other, when no one else in the world does? How do they sacrifice for each other, giving up what they want for what the other needs? How do they make each other feel needed and essential? What beliefs do they share, about what's important and what's not and what's right and what's wrong? These are the things that love is made of.
And though it happens a thousand times a day, you would have to be crazy to give up all that to be with someone beautiful but selfish, duplicitous, and shallow.
Which is pretty much what I said in the thread (though it was more directed to the specific question).