Am I the asshole for being upset my friend made new friends?

So me (15M) and my two friends have been childhood friends for almost 10 years - we'll call them K (14F) and S (14M). We grew up in the same neighborhood and always hung out together. Me and S would butt heads every now and then as friends usually do, but I'd still consider him one of my best friends.

But one day we lost contact with each other. It wasn't any of our faults, we both moved and didn't have a way to communicate anymore (none of us had phones/internet access/etc.). It was really hard for me. I felt lost and alone, and I kinda fell into a depressive state. But despite all that, I still tried my best to try to find my friends again.

Recently, someone helped me track down S. I didn't think I'd ever see him again so I was desperate to meet up. I didn't have any way to contact him to let him know I found him, so I decided to just walk up to him while he was out in public and surprise him. Probably not the best idea, but I didn't have many other options. It ended up working out though. He seemed more shocked than angry that I was there. He even grabbed my face to make sure I was real, which honestly was kinda weird but whatever.

This is where the problem comes in. I was excited to continue our friendship from where we left off, but apparently he didn't agree. I wanted us to team up to try to find K, but I guess while we were separated, he made new friends. He tried introducing me to them, but I ended up leaving without saying goodbye. I didn't like seeing them getting along so well. How was he able to move on so quickly? Did our friendship mean so little to him?

The person who helped me find him agrees with me. She's saying he replaced me and doesn't care about me or K. She's trying to convince me to succumb to the darkness in my heart, and tbh, I kinda want to. So, AITA?