I am sorry to argue with you several days ago.We haven' t talked with each other these days.You are my best friend,aren' t you?
Few days ago when I heard you lost my lovely book,I was really mad,so I argued with you,and said that I could not be your friend from then on.Later,I didn' t sleep well those days.I always remembered a lot of fun we had.So I decided to write a letter to say sorry to you.I also think you should be careful and take good care of your things.Let' s be best friends again,OK?