Having a sibling to fight with means having someone who knows every chapter of your story.

A sibling is the only person who was present for all of it. They were there for the house, the arguments, the version of your parents nobody outside the family ever saw, and the embarrassing years you would rather had no witnesses. That is why they can irritate you faster than anybody else, and why their opinion lands differently. Shared history is not optional and it does not expire.

Use it this week rather than merely enduring it. Ask about something from years ago you have never compared notes on. You will discover you remember the same event completely differently.