Complex sentence: When Garibaldi told Sheridan that he had been drinking for a couple months, Sheridan said that is about what he had suspected, but had tried to deny what was going on.
Split into simpler sentences: When Garibaldi told Sheridan that he had been drinking for a couple months, Sheridan said that is about what he had suspected. Sheridan had suspected that something was wrong for that amount of time, but Sheridan had tried to deny what was probably going on.