I've been telling one "funny family story" for years and I only recently realized I was the asshole in it

My family has this story I've told at holidays, dates, work lunches, pretty much anywhere people start swapping embarrassing childhood memories. It always got laughs, so I never really examined it too hard. The short version is that when I was around 13 my older cousin was staying with us for a few weeks during a rough patch at his house. He was 16, quiet, awkward, and trying way too hard not to be in anybody's way. One afternoon my aunt called the house asking for him, and I answered. I don't even remember why I did this exactly, probably because I was a little shit and wanted to be funny, but I told her he had run away. Not in some obvious joke voice either. I said he'd packed a bag, said he was done with all of us, and left through the back gate like an hour earlier. I still remember how fast she started panicking. She kept asking if I was serious and instead of backing off, I kept going. I added dumb details. Said he looked upset. Said he took cash from the kitchen drawer. Said he told me not to tell anyone where he was going. Then I hung up because I was laughing too hard. What I remembered for years was only the part that came after. My aunt rushing over. My mom yelling. My cousin coming downstairs confused because he'd been in the shower. Everyone realizing what happened. Me getting grounded. Adults being furious for a few hours and then, eventually, the story getting turned into "remember when he was such a little menace." That was the version that stuck. A harmless family legend about me being a chaos goblin kid with "too much imagination." So I kept telling it that way. Last month I was at my sister's place and it somehow came up again. I told it, people laughed, but my sister didn't. Later she told me she always hated that story because I either never knew or pretended not to know what was actually going on back then. My aunt had apparently been genuinely terrified because my cousin had already tried to run away before, and there had been some really ugly stuff happening in their house that I wasn't fully aware of at 13. Not just generic family stress. Real bad stuff. The kind where adults talk in lowered voices and kids only catch pieces. My cousin staying with us wasn't some random visit, it was because things at home were unstable and he wasnt doing well. So when I made that call, I didn't just prank my aunt. I hit the exact worst fear in her life for a laugh. And the part that really makes me feel sick is that I saw it on his face even then. When he came downstairs and figured out what I'd said, he didn't look annoyed. He looked hollow. Embarrassed. Tired. Like I'd taken something private and made it into entertainment without even understanding it. I think because the adults eventually folded it into the "kids do dumb things" pile, I let myself believe that version too. But looking back as an adult, it wasn't one dumb harmless joke. It was cruel, and it was cruel in a very specific way to someone who was already not okay. My cousin and I aren't close now. Not because of just that, life happened, but we never really had much after those years either. I keep wondering if he remembers me as the obnoxious little cousin who made a spectacle out of one of the worst periods of his life, while I was out here using it as a party story. I havent told it since.