Back in '77 or so, when I was 12 and my parents were at the tail end of their 15-year marriage.... After some generically nasty ways they'd treated me one evening, I got an illumination: "They're not on your side." Seems simple. But... who wants to recognize that about their own parents???
It's a terrible thing to understand.
I acknowledged it mentally that night, but then forgot about it... Forgot how to deal with it. Today, at 52, I must remember the clarity of that thought and reality. And deal with it.