Why is it hard for old lost friends to pick up where they left off?

My childhood friend whom I had not seen in ten years, came to visit our town a few days ago. He is a few years older than me. I am in my early thirties. The last time we saw each other, he was introducing his fiance to our group of friends. My cousin and I were moving that same week, so we didnt get a chance to meet her nor say goodbye to him. My mother and father stayed back. In fact, he left town that day I saw him with his fiance. After a year I heard he was married. We grew up together and socialized almost daily. We had a very strange relationship, or less of. He tried hard to get along with my mom and tried to get hold of me. He even said my mom would never allow any guy near me. Even told me I am just like her. One of our last interaction, involved a huge argument between him and my mom. I was so embarrassed listening to them. Anyway, fast foward to a couple days ago, we are part of this big social group. So when we were all talking, I saw my mom talking to him. I walked by and he stretched out his arms for a side hug and said, “have you met my wife?” I told him no. She then tried to hug me. As she did, she told me her name. She is very pretty, and her name is spelled similar to mine. So we smiled at that. Then he asked how my siblings were doing. Didnt ask anything about me. It was a dry awkward moment. Then he and I subconsciously stood side by side watching my mom chatting with another friend, who was standing by. After that day, I kept turning around to find him staring at me with a blank expression, but avoiding me otherwise. I think he left today to go back home to were he moved. No goodbyes. Nothing. Its like we didn’t know each other. So “much” happened many years ago. So it was a weird feeling.