Having endured the death of his younger brother and then the wrongful punishment of Justine which results in her death, Chapter Nine begins by expressing how Victor, feeling incredibly guilty and responsible for these deaths, withdraws from his family and society in general. He is so miserable, in fact, that he contemplates killing himself. However, what stops him from doing so is a feeling of responsibility towards those loved ones whom he would leave behind. He then sees that suicide, though satisfying for himself, would selfishly leave Elizabeth and his father and suriving brother unprotected. Note what he says to justify his reasoning:
Should I by my base desertion leave them exposed and unprotected to the malice of the fiend whom I had let loose among them?
Note how Victor himself sees how selfish suicide would be, calling it a 'base desertion.' He clearly realises that, having given the creature life, he must bear some responsibility towards ensuring that nobody else is hurt as a result of its anger and rage.