It’s a common reading of DH that Ron was simply more vulnerable to the locket than Harry or Hermione because of his insecurities, that the locket targeted Ron for his weaknesses. Obviously, the locket’s torture of Ron was particularly nasty. It tapped into all his worst fears and self doubts. The locket’s attack on Ron was by far the most explicit. But I think we’ve been ignoring the obvious way that the locket targeted Hermione and Harry. It eliminated their greatest source of comfort and hope: Ron.
The locket sees into your heart, your fears, your desires. I think that locket could see that Ron’s loyalty, his support, his lightness and humor, his love were things that Harry and Hermione relied on, both individually, and as a friendship unit. The easiest way to bring down Harry and Hermione was to get rid of Ron.
And it worked. Ron’s departure destabilized the team and put the mission at great risk. There was no forward movement at all on the Horcrux hunt while he was gone. They walked into a fairly obvious trap and nearly died for it. Harry and Hermione’s friendship, which to this point had been been one of the most consistent throughout the entire series, withered without Ron. They were both brought to their lowest moments, each wallowing in their own personal misery, feeling hopeless and getting more and more isolated from each other. This wasn’t by accident, but by design.