Once Victor recovers from the nervous fever he contracted immediately following (and as a result of) the "birth" of his creation, he claims, "I had conceived a violent antipathy even to the name of natural philosophy. When I was otherwise quite restored to health, the sight of a chemical instrument would renew all the agony of my nervous symptoms." In other words, the fear of his creature, the fear of what Victor himself had done, perhaps even the fear of what might happen as a result of his experiment, had caused Victor to turn from his favorite subject, the interest that has sustained him since childhood, in pain.
And although Henry Clerval, his best friend, can tell that Victor is tormented by any reference to his scientific pursuits, Victor says, "I could never persuade myself to confide to him that event which was so often present to my recollection, but which I feared the detail to another would only impress more deeply." Victor works hard to forget what he has done because it causes such anxiety for him, so he cannot even confide in the one person who is most likely to sympathize with and comfort him.