At the end of Frankenstein, Victor has lost his humanity. This is due to the fact that he thinks he has failed at creating the monster. The monster represents a duality in Victor's life: it is both his biggest success in the field of science and also his biggest failure regarding its lack of humanity.
Victor was obsessed with creating the monster, but he never saw it as a pair, as someone who could also have feelings, this is why he never supported it nor educated it, which results in Frankenstein escaping, killing several people and becoming dangerous.
Thus, Victor's search for Frankenstein begins, but this has to do only with the fact that he considers it as a creation of his and his property, and not a human being: he wants to destroy it because of what it has done.
So, we can conclude that the correct answer is B: He becomes obsessed with finding the monster instead of forgiving it.
