Grace Palmieri was one of Wilson's terminal cancer patients who he had a lengthy affair with. These events were revealed in House vs. God.
Grace was diagnosed with liver cancer by Wilson. She was on a great deal of pain medication. However, for her whole life she had dreamed about going to Florence. One day, she had a bad day pain wise so Wilson took her home, and they ended up having sex. Wilson eventually wound up moving in to her apartment after the end of his marriage to Julie Wilson.
When Grace was starting to come to terms with her illness, she encountered a young faith healer patient of House named Boyd. He told her not to be afraid, Wilson was angry because of it, but Chase explained to him that Boyd had just suffered a complex partial seizure. However, after the incident, Grace started feeling better and her tumors shrank, just as if Boyd had healed her. She went to see him multiple times while he was in the hospital.
While treating Boyd, House sent Chase to break into her apartment looking for radiation. Chase found out that she had a boyfriend (from the male clothing in the closet) and was worried that the boyfriend would come home and see him in the apartment. However, House soon figured out that Wilson was the boyfriend, and that he was sleeping with Grace, and told Chase not to worry.
House and his team finally diagnosed Boyd with herpes encephalitis. Grace's "cure" was the result of Boyd touching one of his sores and then touching Grace. The virus went after her tumors first making them shrink. Grace got a few months extra months of life out of it, and she went to Florence. Wilson ended up moving out of her apartment.