When you have to qualify "they may split up" by adding "this time" at the end, it means they should have split up a long, long time ago.

Their marriage should have ended a long, long time ago. They've set a very bad example for you by modeling such a horrible relationship. (That's something I've told parents in bad relationships many times: it's selfish to stay together, because if you stay together your children will be exposed to a bad relationship as their prime example of romance.)

I'm sure they had their reasons. Maybe they mistakenly thought that staying in a terrible relationship is moral and right.

But it's not.

You don't need to feel guilty, no. You may feel guilty regardless, because you can't just boss around your emotions and force yourself to feel fine. But at least on an intellectual level, you've got to know: this dumpster fire of a relationship is because of the choices of your parents, and putting out a dumpster fire is always a good thing.