Is it normal that i dont care about my parents marriage?

My dads been sneaking out at 3 am and sneaking back in at 5 am. It's obvious that he's cheating on my mom, hell I think I know who with too. But the truth is I couldn't care less, I just wish I was a heavy sleeper so I wouldn't wake up each time the door opens/closes. Is this normal? I like my parents, I just think that this is more of their problem rather than mine.