why is it so hard to accept that sometimes friendships just don't last?

I know why it happens, people just drift apart, and that's fine, it's just super depressing reminiscing about how things used to be. I had a friend in 7th grade, we were best friends for years, did EVERYTHING together. But then she started to do some stupid things. I struggled to keep the friendship normal in high school but I had my own personal stuff to deal with and I couldn't be the one to hold it together anymore. Then after I experienced a major loss in my life, very little effort was being put in on her end and eventually we just stopped talking altogether. I hate that it happened and I low key still feel guilty for letting it happen, but I was just exhausted. I'm slowly coming to terms with what happened but sometimes I just get reminded of our friendship and feel bad that it all went south.

~ sorry for the mini sob story, but I just needed to vent for a bit haha