AIO for telling my (M21) ex's (F35) brother she cheated on me with a freshly turned 18 year old?

Her brother messaged me the other night asking what even happened between us and I decided to be truthful about it out of pettiness which I now regret. I feel like a loser for doing so but it all genuinely hurt. It's my first "huge" age gap relationship so we already had all types of looks from both sides of our families and I had just started to fall truly in love when I found out and it was all just so fucking soul crushing. It also doesn't help that this was my first real relationship in almost 3 years. AIO?