I don't know that his life really fell apart, because it turns out his home life was terrible all along, but it definitely shifted how people looked at him. And I went to a small school, so there weren't too many divisions between people (when you only have forty something kids in a grade, "popular" is kind of relative…)
But, a kid's mom decided to leave her husband, the kid's stepdad. The stepdad, who was known to faculty and was considered a "good guy", stopped by the school to deliver something to his stepson. Cool, cool, the secretary gave him a pass to drop it off at the stepson's class, rather than call him down to the office. The stepdad actually had a gun and had no idea where the stepson was during that period, so was roaming the halls. Luckily, a friend of the stepson (who knew what an abusive, dangerous guy the stepdad was) happened to be in the office and alerted everyone. We all went on lockdown, the police came, we were stuck for a couple of hours as they swept the school after arresting the guy. Then, it came out that the kid had been abused for the entire time his mom had been married to the guy, and she only was leaving him after he started hitting her…It was a whole thing, and while everyone had pretty much always liked the kid, he suddenly just had everyone feeling sorry for him. Teachers let him go back and redo assignments to boost his grade. People gave him stuff to "start over." He just kind of got really closed off and stopped joking around and only hung out with like three people after that. He was known as "the abused kid with a stepdad who was going to shoot up a school" and that's hard to get over.