Why did poe wrote his letter of march 19 1827 to john allan?

Edgar Allan Poe wrote a letter to John Allan on the 19th March 1827 to let him know that he was going to leave the latter's house in order to find a place where he could be treated in a better way. He had heard Mr. Allan saying he had no affection for him, so he thought it over for days, and finally reached to the conclusion that that house, was not a good place for him to leave.

On 19th March 1827, Edgar Allan Poe wrote a letter to his foster father John Allan because that day they had the worst quarrel they had ever had and Poe left the family house. He wrote about his determination to find some place where he would be treated well, just the opposite to the way John Allen treated him. John was cruel and he had not even a piece of affection for Edgar.