I've gone through this recently, even though high school was a long time ago for me.
I was recently contacted on Facebook by someone I had not heard from for 50 years. As we talked about HS, I came to learn that something I did, which hurt her, actually had more serious implications than I could have known about at the time.
Yes, I felt guilty. What helped was continued conversation with her -- on social media, in email, and on the phone. She has no ill feelings toward me, and she has helped me to stop beating on myself about it.
I now realize that if we continue to feel bad about what we did back then, and nothing the other person says can change that, then we are showing disrespect for that person in a new way -- we are not allowing them to have grown since HS, in our minds. We keep sticking them in the past. They are not in the past though; we need to accept who they have become, and not hold onto who they were.
Self-forgiveness can be very difficult. I do hope you can find it someday!
