You have lovely handwriting!
People come into our lives for a reason. Holding too tight can just ruin things. It's sad - I have plenty of friends who just disappeared when I thought they were for life - but I think just remembering the good things is enough. It's odd though that she just 'switched' like that - you must have spent ages trying to figure out what went wrong!
Once I had a friend who got really angry with me that I changed plans last minute. All it was was changing the meeting place, not the time or the meeting itself. She just lost it. I was stunned. She cut all contact with me. Apparently I always changed my mind and it wasn't fair on her. I spent weeks feeling upset about it and feeling that there was something wrong with me.
But then I have plenty of friends that love my changeability and understand it. They know it's an essential part of my nature and I don't mean harm by it. In the end, I had to just let it go. It certainly felt like an extreme reaction to a small thing, but it must have been a big deal to her.
People come, people go. The best ones stick around.