He is not interested in another woman, he just wants to live the single life again. He decides to divorce Mary. John's attitude is like that of so many self-centered people in today's world. He seems to labor under the illusion that he can abandon the most sacred of human relationships, simply at his own whim. The attitude is one of consummate selfishness and stands in opposition to a number of biblical principles.
Marriage is a life-long commitment.
The Bible is clear on the matter of the perpetual design of the marriage union. God is the Author of the marriage institution. It is, therefore, only the Creator who may determine when a divorce proceeding may be initiated. Just as no person is eligible to marry without the sanction of divine law, in like manner, no one is free to divorce without the authority to do so. Read the catalog of sins mentioned in this context for some idea of how God views such a transgression.