People change, that's life. Nothing ever stays the same. It's kind of like taking a photograph of a tree and capturing that specific moment when the breeze hits it just right, or as a leaf drifts away. You can never recreate that specific moment. That's how life is, we as people are constantly changing.
It's sad to think about it but most relationships end. Whether is was a friendship, a significant other, or another type of relationship. People move, people die, people lose touch with each other.
I'd be lying if I said I was the same person that I was in high school. I'm so not the same person as I was even a couple months ago. My tastes in everything have changed, my style, my favorite music. Even something as simple as the genre of books I read has changed. I've changed my hair color/cut I don't even know how many times in just the past semester.
Some people don't believe that other people change but they do. After a relationship has past it's expiration date you don't know that person anymore. You knew them. There is a difference. My pet peeve is when I find out someone from my past says that they "know me", when they don't know me anymore. You knew me as I once was, I've changed and for someone people that's a hard concept to grasp.
It's ok to let go of people. Friendships come and go. If you're lucky you might have one friend that sticks with you your entire life but for most people that isn't the case. It saddens me to say that I'm only in contact with two of my high school friends. I say in contact very loosely because we're not super close anymore. Occasionally we'll hangout or text but we don't have that close connection that we had before we left for different colleges.
You also shouldn't feel guilty about moving on and cutting the toxic people out of your life. I think almost everyone has had a toxic friend; that one "friend" who always has to start drama or feels the need to bring you down to make themselves feel better. Just cut out the toxic people and your life with be so much better. Trust me I know from experience.
Moving on from certain people you use to be close with can be scary but sometimes it's for the best. You will meet other people you align with more and then you might change again; then you can meet even more new people. Even though you change as a person and the people you were once close with change too, you'll always have the memories of each other.