Later he wants to completely forget about the monster but the monster will not let him to forget.

THE POOREST CREATURE

“Alas! I had turned loose into the world a depraved wretch whose delight was in carnage and misery.” After the first murder, it is clear that the monster has a special aim: to let his creator suffer in the worst way - by killing all his relatives. But how did he know about his creator and how did he find him?
“At first I started back, unable to believe that it was indeed I who was reflected in the mirror; and when I became fully convinced that I was in reality the monster that I am...” In spite of his appearance he is one of the most intelligent and skilled creature in the world. I will explain it. When he is “born”, there is nobody to take care of him as it is natural, let us say in the world of mammals. He realizes that he has several senses but he does not know how to use them and what is their purpose. He has needs for drink, food, sleep and for sentiments, as he later finds out. Without any help he is able to cope with these things and learn a lot about the secret of life. He spends several years very close to a group of people. He learns to talk and read by watching them doing it. He realizes that he is lonely, has no relatives or friends - things necessary for a happy life. In the beginnings of his life, he is a very sensitive and sensible being, loves and helps the people who he is watching. But as the time goes on he is more and more thinking about his life (who is he, where does he come from) and he is getting more and more depressed and frustrated. Then one day he tries to contact the people but the result is a disaster. From then his behavior changes. “My daily vows rose for revenge - a deep and deadly revenge, such as would alone compensate for the outrages and anguish I had endured.” He reads the notes, which he has found in the Frankenstein’s coat and starts to plan the revenge.
"You must create a female for me with whom I can live in the interchange of those sympathies necessary for my being.” The monster is extremely unhappy with his life and feels that he must have a similar being on his side. In this situation, the attitude of Frankenstein changes for a while. He feels that he is responsible for the monster’s melancholy. He agrees that he will create him a partner but later he changes his mind because he realizes that she-monster can be as virulent as the monster is. He also feels an enormous responsibility to the whole mankind.
“You are my creator, but I am your master; obey!" These are the strongest words in the story and it is clear that the final fight between them is about to come. Frankenstein is very egoistic - he is sure that the monster wants to kill only him; but he finds crueler way how to avenge.