It's interesting to read people's viewpoints...
especially as I left my wife of nearly 14 years only 4 weeks ago
Although every situation is different - there are always similarities. Don't forget that while it's necessary to fall in love to become married (okay, perhaps not necessary per se, but usually important!) it's also possible to fall out of love. Outside influences can affect this, but at the end of the day, it's your head and heart that tell you what is right, and what isn't.
It's the same if you choose to embark on an affair (which, I hasten to add, is NOT the reason I chose to leave) - your head, and your heart, make the decisions.
Going back to Sarah's point about the character being too busy, forgetting anniversaries etc - that isn't necessarily a recipe for divorce, if the person has always been like that then often allowances are made, or they may even make up for it in other ways? I always, without fail, remembered anniversary, birthday, Xmas, Valentines Day.... would often buy flowers at the weekend for no reason, etc etc... BUT if the two people in the relationship drift apart, for whatever reason, then no amount of face value gifts will keep them together.
That's exactly what happened with my wife and I - she will say that she didn't fall out of love, it was only me - and that may well be correct. But we met 19 years ago, when I was 20 and she was 33 - 19 years later we are very different people - some people grow together over time, ties bind them, until they are a single functioning unit. Other people stay as two separate entities - and as far as I can see that's a recipe for either a split, or an "open" marriage with all that entails. As far as I'm concerned we very obviously drifted apart - i'll take some responsibility for that, but not all. As I reach 40 I'm making a conscious effort to be a better person, fitter, healthier, and hopefully happier - that didn't necessarily sit well with an overweight, smoker and drinker. Yes, she was like that when we met, and always has been, but as people change, then thought processes, priorities, even attractions change - and if you change, but the person you're with doesn't - then either you have to accept that, live a compromise (that won't necessarily make either of you happy), persuade them to change - or decide to make a very drastic change to your relationship.
After 9 months of turmoil, unhappiness, deep thoughts, occasional depression, and odd hints of bright sunshine as ideas of another possible life were shown to me I made what I consider a brave step - to walk away from families, friends, an easy life, a house, comfortable finances - to find what will make me happy. Selfish? Maybe, but we only get one life to live, and marriage should be a joyful celebration, not a cell.... if it becomes a cell then it's time to consider what you can do to break through the bars...
Sorry if it's an unfocused ramble, but I write as I think...