After living alongside the family in the cottage and learning the language and gaining knowledge through reading Frankenstein’s creation starts to yearn for friendship. He decides to appeal to the family he has grown to love and visits the blind father when the rest of the household are out walking in the woods.
But he is discovered in the cottage and the horror he is hit and screamed at and leaves the house heart broken. He decides that he will seek revenge on mankind and starts to turn to violence. But what stays his hand is the idea that the responsibility for solving his problems with companionship reside with his creator.
He sets out to find Frankenstein and comes across his youngest brother and cannot resist the revengeful urge to kill him then use his cunning to frame the servant girl. That ends his story and his demands from Frankenstein are that he creates a female mate for him.
Having heard the sad story presumably Frankenstein feels some responsibility but the fact remains that the monster he created has killed his brother and the grief and anger in the young doctor is still raw enough to cloud his judgement.