I left my husband when my 2 boys were 3 and 1. I recently posted a similar answer in the "looking ofter yourself with a baby" under the title of " I thought our baby would save our marriage" so have a look and email me if you want to chat.
In my opinion, staying just for the childrens sake is one of the biggest mistakes anyone can make. I know of many friends who's parents stayed together until they were in high school and they all would have rather it happen when they were younger. You end up growing up with the notion that your childhood was one big lie and it hurts!
In my situation, leaving my husband was for the best.
I did and still do believe in the sanctity of marriage but in my situation, I had to leave as it was distuctive to me and the children.
I am currently with a beautiful man with whom I just had another baby to and we will get married next year.
Goodluck with your choices and email at [email protected]
if you want to chat. smile