What am I supposed to do with this knowledge?

(Editors note, this is based off a story I wrote when I was 9-10 years old that I'm now retelling in the POV of one of the characters) Back when my sister was a freshman in high school she dated a guy named Kyle. I got along with him and he was genuinely fun to hang around. Then one day he and my sister had a huge falling out and refused to see each other again. My sister moved on. She met a new guy named Brandon who as of today is now my brother-in-law and they have a daughter together. Kyle however still held a grudge against my sister for the reasons they broke up. About a year ago Kyle and my sister had another huge fight and at the end of it Kyle had an emotional breakdown, apologized, and actually tried to change for the better. My sister luckily has a heart of gold and forgave him. (Editors note, I made her daughter the same age as me, and as of when I originally wrote all this I was 9 turning 10 in a few months, meaning Kyle has been holding this grudge against his sister for over a decade) Kyle eventually found his own support group of friends who knew about all the horrible things he's done and still chose to be friends with him anyways. 6 months later my sister introduced me to this girl named Athena who she became friends with and I immediately fell for her. She may seem emotionless at first glance but she has a heart of gold. 5 months later, it was nearly Valentines day so I made a plan to ask her out on a date. After we made the plan through text, I heard a knock on the door and when I answered, Kyle was there. Now keep in mind I knew he and my sister made up, but this was the first time I'd seen Kyle in person since he and my sister originally broke up, so seeing him in person again for the first time in 2 decades hit with such a huge wave of nostalgia. He arrived for a surprise visit, but my sister wasn't home so he took the time to catch up and bond with me instead and I realized how much I missed him. He was still as snarky as the day I last saw him. He then invited me over to his place so I could meet his group of friends. On the way there, he asked me about Athena, and I immediately questioned how he knew Athena considering I only met her 5 months ago. Then he spelt it out for me: Before he and my sister began dating, he used to date Athena. Meaning I'm now seeing the ex of my sisters ex.