After having that previous paragraph written for over a week, I finally realized who I ought to write to, so here it goes...
You've been my best friend for nearly four years now. We've helped each other through rough patches, had some of the greatest adventures, and survived living together. You are awesome. Because of you I feel as though I've had someone to lean on, someone to laugh with, someone to pick me up when I feel like I've hit rock bottom. You don't judge me when I do stupid things or cry over boys or mess up pretty bad. You've listened to my concerns about life and in turn trusted me with your secrets. I'm lucky to know you, to be friends with you, to have developed such a good relationship with you.
Becoming friends/roommates with you was one of the best decisions of my life. Thanks for being my best friend.