Lonesome Dove, Volume 2: Comanche Moon by Larry McMurtry

THE MORNING AFTER Nellie's funeral, Augustus McCrae disappeared. He had been seen the night before, drinking in his usual saloon, but when morning came he was nowhere to be found. His favorite horse, a black mare, was not in the stables, and there was no sign that he had been back to the room where he had lived with Nellie.

Call was surprised, and a little disturbed. When Geneva, his first wife, died, Gus had sought company wherever he could find it. He stayed in the saloons or the whorehouses for over two weeks, and was hardly fit for rangering duties once he did resume them. On a trip to Laredo, where banditry had been especially rife, he had been thrown from his horse three times, due to inebriation. The fact that he had chosen a half-broken, untrustworthy horse for the ride to Laredo was evidence that his mind was not on his work. Augustus had always been careful to choose gentle, well-broken mounts.