Dear Jean,
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?
Yours ever,
Vince