If you haven't been divorced...please make one up and also an understandable reason.
"Well cause your dad is a complete idiot" is not a route I would recommend. I have never been married but when I ended things with the kids dad who didn't take to kindly to that that was what flew out of my mouth that day.
It can't be helped. What else are you gonna say..."Because I've been an idiot?" ...would not be the truth, either.....
I was kinda feeling like an idiot for putting up with what I did for so long
I have a fair amount of friends who have divorced parents, there is no good way to tell them that their parents don't love each other anymore, thankfully my parents are far away from such thoughts, I hope I never have to deal with divorce.