Junior marketing manager,
Dear Ms Rebecca,
I, Joseph Alls, would like to take this opportunity to apologize for my recent behavior with you. I am going through some critical and rough times of my life and which is what can be clearly observed in my behavioral conduct, however, this is no excuse for my entire misdemeanor. And therefore I express my heartfelt regret for the same.
You not only shouldered my responsibilities along with yours, but also calmed me in these tough times. I must appreciate you for all your efforts and assure you a much mature and dignified behavior henceforth.