Fife,
I agree with Lillie on the affect of divorce being much greater on adult kids than on young children. If you're staying for the sake of your kids, it would be advantagious to find out if that is really the best for them.
What if you stayed all those years, and then left, thinking they would be okay, since they are older, and now able to take care of themselves. That may be the problem right there. When they have left the house, they won't have either parent to guide them through their feelings of loss.
Maybe you could check out the book by James Dobson, "Life on the Edge". This book addresses kids from the age of 18 to 24. He believes this is one of the most critical times in a person's life.