What does Proverbs 5:9 mean?

One result of committing adultery is to "give your honor to others." The person who succumbs to the temptation to commit adultery loses his reputation. It's interesting that even in the modern era of promiscuity and casual sex, violating a marriage is still a mark of shame. Adultery can bring social stigmas of weakness, or cruelty, or both. This brings a separation—sometimes very literally—from other people.

Beyond that, those caught in adultery risk spending the rest of their lives in the company of such people: seducers and their associates, all of whom are cruel. The world is only interested in using the seduced person as a target of their abuse. "Mercy," in that scheme, means nothing.

Certainly, the prodigal son learned this lesson the hard way. He squandered his money on reckless living (Luke 15:13). His sinful lifestyle left him penniless, homeless, and hungry. Finally, he found a job, but it was humiliating. He worked as a hired man in the fields feeding pigs. He was starving to the point that he was tempted to eat the slop given to the pigs (Luke 15:13–16). Thankfully, the prodigal son learned that it is never too late for forgiveness, so long as a person is still alive (Luke 15:20). The world is merciless, but God is merciful to forgive those who turn to Him in faith (Hebrews 4:16). That does not change, at all, the fact that succumbing to temptation ruined the prodigal's life, and drastically changed his prospects.