AITA for not forgiving the guy who hurt my Pokémon years ago even though he’s a better person now?

Years ago I (17M currently) took on the Gym Challenge in my region and was doing pretty good so far up until I reached a certain gym leader. I had gotten cocky admittedly and had been boasting about my Houndoom being able to take down his entire team, but when I got there he defeated me with a single Pokémon and ended up putting her in serious condition. He said things to me that stuck with me even to this day and to make matter worse my brother (20M) called me weak and beat me up for losing to what he called “An easy win” so I decided to travel to different regions to collect badges in order to prove I was strong

Now years later after training and collecting badges I finally returned to my region looking for the gym leader, but when I met him he was a completely different person! He said he regretted doing what he did and that he was sorry, but that just made me more pissed. I can see that he truly regrets what he did in his past but I can’t bring myself to forgive him even if he has gotten better, so I ask AITA?

TL;DR Gym Leader hurt my Pokémon and after years of planning my revenge the guy has gotten better and is truly sorry, but I can’t forgive him.