How not to leave your wife
Don't tell her you haven't loved her for X years. She doesn't need to know this.
Don't tell her you're not attracted to her body type. Bad enough you're leaving her - why destroy her self-esteem.
Don't tell her you're scrogging a 21-year-old co-ed. Yeah, she'll find out eventually, but she doesn't need to hear it now.
I'm sure there are more, but those are the mistakes one of my old high school friends recently made. At least IMO.
Divorce is no big deal when there aren't any kids or they're older. When you have small kids it should be an absolute last resort. Suck it up!

UPDATE:
Okay, just looking back over my posts and I'm laughing at my contradictory statements. In this post I'm dogging my buddy for leaving his kids. In a previous post (July 3) I stated that I thought my wife's friend should divorce her husband.

To try to clarify - I DO think divorce should be a last resort and a certain amount of sucking-it-up is sometimes necessary. But I also don't think you do your kids much of a favor if you continue in a marriage where you can't stand your spouse - where you come to despise them.

My high school buddy was probably at that point, and so it may well be for the best. And my wife’s friend has been separated for two years – her kids are already used to it.