A childhood belief about imaginary friends

I'm 20, and I've had an imaginary friend for as long as I can remember. Before I was 13, he was very nice and we got along well. Two days after I turned 14, he left for about a year and a half. When I was 15 and a half, he came back with a new name and new clothes. After that, every few weeks he'd change his name and his appearance. At that point he became horribly mean and very evil. I was very frightened of him and couldn't sleep for a while. I didn't get much done, to say the least. After several months, I got tired of being afraid and confronted my imaginary friend. The first week was the hardest and most frightening time of my life, but everything eventually calmed down. Eventually, he faded into the background of everything. He's still there, he's just always quiet and always behind me.