It’s no spoiler to reveal that Ruth Ellis (Lucy Boynton), the lead character in the new four-episode crime show A Cruel Love, died by hanging on July 13, 1955. Ruth was a real woman who committed a very real crime: She shot her lover, David Blakely (Laurie Davidson), on Easter the year of her death. But what led the nightclub hostess to carry out such a horrible act? That’s the question behind A Cruel Love, BritBox’s excellent true-crime drama that explores Ruth’s motivations behind David’s murder, the subsequent trial that dominated the tabloid press and her death by execution, which is still the last time a woman was put to death for her…