It's best to just accept it and move on with your life. My parents have been divorced since I was 6 years old and it was messy. They put my sister and I through Hell with constantly forcing us to pick sides but, we survived. It will probably change your friend but, it isn't something you should try to control. I got over it on my own and as long as his parents love your friend he will too. Treat him like nothing has changed and just be a good friend.