If it's any consolation, my daughter was 6 months old when my ex left. She is now 9, extremely bright, kind hearted, animated, happy little girl who loves life.
I read an article once of parents who stayed together for the kids. Every last one of them said they wished their parents had divorced because of the unhealthy dynamic they witnessed between their parents and/or fighting.
Yes, I know what you are going to say, if we could just stay together and build a healthy marriage that would be best. But it's not an option on the table. And not only one person can make that happen.
So it's okay to feel sad for your child. Mine still gets upset sometimes when she misses her dad. But it is not destroying her life in the least bit.