On a rainy October night in Washington, D.C., the friends and family of Jeremy Blake gathered for a private memorial service at the Corcoran Gallery of Art. Blake, an art-world star acclaimed for his lush and moody “moving paintings,” shape-shifting innovations mixing abstract painting and digital film, had ended his life on the night of July 17, walking into the Atlantic Ocean off Rockaway Beach, Queens, never to return.

“I am going to join the lovely Theresa,” Blake, 35, had written on the back of a business card, which he left on the beach, along with his clothes. Police helicopters searched for him for days on the chance he might still be alive. Friends prayed that he was, talking of how his passport was missing, he had bought a ticket to Germany. Then on July 22, a fisherman found his body floating 4.5 miles off Sea Girt, New Jersey.

“The lovely Theresa” was Theresa Duncan, a writer, filmmaker, computer-game creator, and Blake’s girlfriend of 12 years. He had found her lifeless body on July 10, in the rectory of St. Mark’s Church in Manhattan’s East Village, where the couple had been renting an apartment. There was a bowl full of Benadryl pills, a bottle of Tylenol PM, and a champagne glass on the nightstand. There was a note saying, “I love all of you.” Duncan was 40. The last post on her blog, “The Wit of the Staircase,” was a quote from author Reynolds Price about the human need for storytelling and the impossibility of surviving in silence.

No one who spoke at Blake’s memorial service that evening at the Corcoran said anything about Theresa Duncan. Almost no one mentioned her name. (It happened to be her birthday, October 26.) No one talked about the dark stories and wild speculation that had emerged after news of the couple’s “double suicide” hit the media. There had been reports they had become “paranoid,” obsessed with conspiracy theories, believing they were being harassed by Scientologists. The Internet fi...