Asking Eric: Neighbor told my boyfriend I hurt her feelings, but won’t say what I did. Now what?

A woman is facing a conflict with her neighbor, who informed the woman's boyfriend that her feelings were hurt. However, the neighbor swore the boyfriend to secrecy, preventing him from disclosing the specific cause of the anger. The woman feels unable to address the issue directly without exposing her boyfriend's breach of the neighbor's wishes. She now seeks guidance on how to repair the relationship despite not knowing what caused the offense.