> Note his forceful denials of an affair at the end, which we now know to be false.

Do we? Do we know that an affair (as opposed to an unconsummated infatuation) existed at the time of the letter, as opposed to later? A quick googling indicates that Miss Ternan may or may not have returned his affections.

Despite what various public figures would have one believe, it is possible (if not terribly probable) to resist temptation…