I cant seem to move on..

Someone who i was good friends with until last month due to their own decisions in life. Is still in my head and i cant seem to move on! I keep going back to its not their fault entirely and trying to understand all the reasons or possibilities why they just left and ghosted me. The natural response of getting angry and hating them barely come out and its annoying cause it would help me forget them quicker. Im tired of thinking about them. I wish i didnt care so much 😩