A zipper that separates behind the zipper slider is a very common zipper failure mode, esp. on tents, backpacks and luggage. It's an easy fix with
How to Re-Align the Zipper on a Backpack - iFixit Repair Guide
Broken Zipper On Luggage Replacement - iFixit Repair Guide
Zipper Insertion Pin Replacement - iFixit Repair Guide
How to Fix a Broken Zipper - iFixit Repair Guide
how to fix zipper that came off –
5 Ways to Fix a Broken Zipper - wikiHow
Replace a jacket zipper (without unraveling) - iFixit Repair Guide
Zipper Repair Kit
Jean Zipper Repair - iFixit Repair Guide