A person I thought I knew

I had this this person who I considered as a friend. Turns out, it was all one sided, and looking back at all of our memories just brings pain and regret to myself. I gave so much into the friendship, helping her through losses of friendships, difficult relationships, and even set aside the pain she had caused me to help solve her pain. I set aside all of the pain she had caused me because I truly thought that she had changed, only to be thrown away from her when she found someone new to be friends with.