go off with someone
phrasal verb with go verb uk/ɡəʊ/ us/ɡoʊ/ going | went | gone
移情别恋于（某人）
to leave a wife, husband, or partner in order to have a sexual or romantic relationship with someone else
Did you know that Hugh had gone off with his sister-in-law? 你知不知道休跟他的嫂子好上了？