I don't think it's just the money that keeps them together, as some people seem to insinuate. 
Yes, it's fair to say she should leave him. But I can see things from her perspective, too. They've been together for... like... ever. I mean, they met as kids before they were even teenagers. They grew up together, and given their ages when they started dating, one has to assume he was her first 'real' love (of course, she may have had crushes on Hollywood stars before him).
There are plenty of people around who are not famous and are still with people they have been with forever when others may think they shouldn't be. Not because of money, but simply because it's bloody terrifying turning your (and your kids') life upside down, plus... there's also this thing called 'nostalgia'.
If you've known someone for so long, you probably think you know them better than anyone else. Better than any woman he could have a fling with. And deep inside, you think that deep inside that imperfect man standing before you now, there's still that boy that you fell in love with more than a decade ago, with whom you went through good times and bad... and you just don't know whether other men out there would actually be any better than him (especially when you move in the circles Coleen moves in).