My mom has been married 5 times. I was nearly 8 when she left her second husband-- my adoptive dad-- and married my stepfather. It was hard and confusing because my father was openly sad while my mom was pretty happy (maybe?) and pregnant with Husband#3-to-be's baby.
Her infidelities are why most of her marriages split up. Either they were the problem or facilitated her leaving.
My mom would be the poster parent for what NOT to do to your kids in regard to divorce. She regularly told my sister and I that we could choose which parent to live with, which was horrible and made us feel guilty. She regularly bad-mouthed him; if he ever took me to the doctor, she'd throw the medicine away because it "wasn't right". She encouraged me to write a letter to my father's then-fiancee to tell her not to marry him because he was a 'thief' (he had taken a couple ashtrays from casinos...). When he was late to pick up, or was called away to National Guard service fighting forest fires, she let us know that he was 'choosing' other things before us.
With the next divorce, she just blamed all of that one on me. :)~ Sadly, that was the family party line for years to come.
What's most painful is that I had a truly awful, no-win situation with some adults who refused to take responsibility for their own actions. The divorces were hard to get past in some ways, and I did a lot of work around this in my 20-30s. Now, what's left is a lot of sadness that this all actually happened and that, in her pain and mental illness, our mother made us tools against our parent as well as each other. My take-away from this was a lot of strength, growing and healing I had to value and pursue on my own. In this way, dealing with those terrible circumstances became an opportunity to become a better person.
Below, you have a lot of posters whose parents really tried to do the best they could for divorce. I write this so you can see that it really is how the parents handle things which has the most direct impact on the children. (I just scrolled down and agree with NYMetroMom's answer-- my mother's mental illness destroyed our family. Had both parents been relatively emotionally healthy, things would have been a lot different.)