NOTE:  A "correction" would be very hard, so I'm going to rewrite this as I would have written it.

To my friend

Dear friend,
I still miss you although I know it won't change anything.  Still, I don't think that our last conversation was the end.  I remember that you promised to talk to me the next day, but you didn't make it and now it seems like you simply disappeared.  Since I don't know what happened to you, I have been very worried. 
It has been more than a month since we last talked.  I haven't heard from you, and I really want to figure out why.  I just can't accept the truth that you are gone.  Sometimes I wonder why you wouldn't tell me directly if you had finished helping me.  You couldn't have just disappeared that way.  I truly enjoyed our talks and I know you felt that way, too.  Even though I made so many mistakes in my broken sentences, you never complained.  Instead, you just corrected me in a friendly way.  This is why I have been so grateful to you.  Sometimes we talked about those tiny things in our lives, and changed our opinions about them.  We talked about the people we met, the things that were going on at home and at work, and even the movies we watched. 
It seems we have some things in common.  We both like music, movies, and even spending some quiet time alone after work (we agreed that it is a good way to clear our mind).  We are both indoorsy and not into social activities. 
You were one who I felt comfortable talking with.  I dared to tell you how I felt about the people around me, that they are mean, selfish, shallow, and prideful.  I have never felt so comfortable talking to anyone like this before.  I can't accept that I have lost you as a great friend.  Now I am trying to write something that I can refer to later, in case some day I forget everything due to aging.  I'm pretty sure time will take away everything no matter how much it is meant to be. 
Thank you, my dear friend.  I wish the best for you, always.