The Fourth Circuit has held that a woman who was threatened by the murderers of her common law husband. Specifically, the court recognized that the applicant was more likely than others to investigate her common law husband's death and report his death to the police because of her family relationship to him. As such, her family relationship was one central reason for her persecution. This caselaw is excellent precedent for expanding family-based social groups to include co-habitating domestic partners.
The full text of Cantinallo Cruz v. Sessions can be found here: