Dear Sid,
For a while now I have noticed a change in your behavior, you have been acting differently and I would like for you to make a change to your actions please.
I have noticed you have become careless about things and that you are just moving in such a bad company, which has made me feel so horrible for you. I hope when you receive this letter, you listen and use what I said for the better.
best of,
(Your name)