Dear Wang Xin,
I have been sorry that you were so upset during the morning.I have tried to talk with you about it,however you rejected me.I did not know what happened to you,but I really want you to know that no matter what occurred,I am with you because you are my best friend.Of course,you can talk with me whenever you want and I believe everything will be just fine.Don't be too worry.By the way,maybe we can have dinner together sometime,and it will be a better chance to communicate because there are always too many people in the classroom.
Best regards,
Yours truly XX.