What does Judges 15:2 mean?

One role of a father during this time was to negotiate advantageous marriages for the family. That included ensuring his daughter's interests were protected as that marriage began. In some cases, it was common for a daughter to continue to live at home for several months after the wedding while moving preparations were made. The groom would visit periodically, and the family would hope to see the daughter become pregnant during this time.

Samson left from his own wedding feast in a horrific rage (Judges 14:16–19). He apparently did not communicate whether he would return. His wife had betrayed his trust, though it's unclear if Samson knew she did so under threats to her life. In the aftermath of Samson's departure, the woman's father was in a tricky position. If Samson was not coming back, his daughter might soon become an abandoned woman, unworthy of marriage in the eyes of that society. To prevent her from suffering that fate, her father married her to one of the local men of Timnah (Judges 14:20). In fact, this man was one of the thirty who threatened to kill her and her family if she did not give them Samson's secret (Judges 14:15). How soon he made this choice is not explained, but there was likely not much delay.

Unfortunately for everyone involved, Samson has returned. He believes he is still legally married to the woman and plans to sleep with his wife. Details of the story don't make it clear if he had already consummated the marriage, or if that was meant to follow the seven day feast he'd abandoned. Her father explains that he thought Samson hated her after she betrayed him, so he gave Samson's wife to someone else.

Hoping to quickly make things right with Samson and marry off another daughter, the father offers the bride's younger sister to Samson as a wife. He claims the younger one is even more beautiful than her sister. Samson will not even respond to this offer.