Or, you know, distance, being an adult, having a ton of responsibilities. That's a big reason a lot of people end up in this situation.
Life tends to happen. It doesn't always mean people dislike you or don't want to be your friend, or that you did something.
I don't talk to most of my "close" friends from college anymore. After we graduated and were still all good friends I would text them and try to stay in contact with all of them. They didn't. Years later got back into contact with them and found out, they just got really busy after college trying to build a life.
Assuming OP has anything to do with why they don't talk to him is naive. It's like people have never been to college or had friends that dropped by the wayside.
This shit happens. And it's usually a result of getting busy and living life and "out of sight out of mind" taking place. Not "fuck that guy I don't like him anymore and I just won't bother telling him" after 10+ years of friendship.