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The nearer I approached to your habitation, the more deeply did I feel the spirit of revenge enkindled in my heart. (16.17)
When you think about it, it totally sounds like the monster has a crush on Frankenstein: he even gets nervous and fired up when he closes in on the love/hate of his life.
All was again silent, but his words rang in my ears. I burned with rage to pursue the murderer of my peace and precipitate him into the ocean. I walked up and down my room hastily and perturbed, while my imagination conjured up a thousand images to torment and sting me. Why had I not followed him and closed with him in mortal strife? But I had suffered him to depart, and he had directed his course towards the mainland. I shuddered to think who might be the next victim sacrificed to his insatiate revenge. And then I thought again of his words -- "I WILL BE WITH YOU ON YOUR WEDDING-NIGHT." That, then, was the period fixed for the fulfillment of my destiny. In that hour I should die and at once satisfy and extinguish his malice. The prospect did not move me to fear; yet when I thought of my beloved Elizabeth, of her tears and endless sorrow, when she should find her lover so barbarously snatched from her, tears, the first I had shed for many months, streamed from my eyes, and I resolved not to fall before my enemy without a bitter struggle. (20.16)
Victor thinks that the monster's revenge is "insatiate"—that it'll never be satisfied. He's wrong. It will be satisfied, just as soon as he kills off everyone Victor has ever cared about.
This letter revived in my memory what I had before forgotten, the threat of the fiend--"I WILL BE WITH YOU ON YOUR WEDDING-NIGHT!" Such was my sentence, and on that night would the daemon employ every art to destroy me and tear me from the glimpse of happiness which promised partly to console my sufferings. On that night he had determined to consummate his crimes by my death. Well, be it so; a deadly struggle would then assuredly take place, in which if he were victorious I should be at peace and his power over me be at an end. If he were vanquished, I should be a free man. Alas! What freedom? Such as the peasant enjoys when his family have been massacred before his eyes, his cottage burnt, his lands laid waste, and he is turned adrift, homeless, penniless, and alone, but free. Such would be my liberty except that in my Elizabeth I possessed a treasure, alas, balanced by those horrors of remorse and guilt which would pursue me until death. (22.14)
Victor is afraid of pulling Elizabeth into his destructive interactions with the monster, but his obsession will not give him peace.