Lincoln is seen by several otherwise-reputable scholars as homosexual because of differences between how we see sexual relations now vs. then. In the 19th century US it was more common for men to sleep together while they were traveling, especially in the legal profession. Two men sleeping together in the 19th century US wouldn't have had the sexual implications it has now. Lincoln was a lawyer in rural Illinois and had to "ride circuit" and follow presiding judges through different towns trying cases. Rural areas lacked the motels and travel infrastructure they have now, forcing the poor and business travelers to share lodgings. That is how Lincoln met Joshua Speed, who lived with him and shared a bed for 4 years. The bodyguard you mentioned, David Derickson, slept in the same bed as Lincoln when Mary Todd was away. But considering he had been married twice with 10 children by then, his sleeping arrangements with Lincoln are probably more indicative of the president's insomnia and clinical depression than his sexuality.

Sources: Team of Rivals Doris Kearns Goodwin The Intimate World of Abraham Lincoln Clarence Tripp