Many people believe that forgiving and forgetting is the best method, or that we need to let go of things from our past in order to move on and make room for the new things we are going to experience in life. Although that may be helpful for some, I don't believe that is how it works. I don't think letting go of memories or the people in them is the only way to move on, I think acceptance is the answer. There's not much you can gain from completely erasing people or your experiences, if anything, that can be a loss in its own.
You learn from your past, you learn from those you've experienced with, you learn from the hurt just as well as you learn from the happiness you endure. How do you know what you want or what you need if you never experience the things that helped you figure those things out? Of course, there are people who may be toxic, people who do nothing but bring you down and bring nothing beneficial or positive to your life, but those are the people you still learn from. I do believe that every person who has somewhat impacted your life, in both a positive and negative way, those people help shape you, not define you, but definitely leave their mark.
It's important to look back on your past and either appreciate it or learn from it, learn from your mistakes, maybe even think about what you could have done differently. You shouldn't have to let go of everything, you learn from your past, you grow from it. Accept that. Cut out the negative, but learn from it. Any heartbreak, any loss, any fight you've had with a friend, any thing that may linger in your mind, don't push it away. Acceptance is key, and of course just like anything, it is easier said than done. Don't feel guilty about your past and don't feel guilty about dwelling on it. If something is still on your mind after a long period of time, there's a reason for it to be. It is OK.