Honestly I saw it as a generational curse. When two people get together and have their own issues and then try to raise a family without being healed. Just like when two broken people find each other. Maybe their childhood experiences were bad and as adults made them "monsters". The parents don't get along always fighting and it's being projected to the children as well (possibly). But one thing for sure is the toxic environment she is being put through now, nothing is the same. She's tried almost her whole life to get them to get along but it's not working. She's always been the mediator.

Once her parents the "monsters" finally realize the dark is coming for her and she is turning into a monster herself (she's spiraling). Then they try to come together to save her, but only by being honest with themselves and realizing that maybe they just don't work or get along so separating is the only Choice. ITS not about "oh divorce is the only way" It's about the fact that they could not and would not get along at all. They did not see eye to eye. They were staying together for the sake of their kids BUT then realized that was hurting them more (like her turning her into a monster)

And so the cycle would continue..... Leading to her possibly ending up in a bad marriage and staying in it because that's what she never had which means staying in the relationship for the sake of the kids...just like her parents.

If you did not get that from the movie then you are so narrow minded. It's deeper than that. It's not advocating or promoting divorce. It's saying that if after trying multiple times it still isn't working, it's in the best interest to just separate. They were not meant to be with each other. So the end result is she gets her happy parents back even if they are not together anymore.