When Megan McAllister initially chose to stand by her fiancé, Philip Markoff, many questioned why, given the charges he faces, she would defend him.

Markoff was given the catchy but unenviable nickname of “the Craigslist Killer” after allegedly trolling the erotic services section of the site for victims, luring them to hotel rooms, binding their hands with plastic cuffs and robbing them at gunpoint.

He is accused of killing New York masseuse Julissa Brisman in a Boston hotel room after she resisted.

McAllister, it appears, did what many do after a relationship takes a traumatic turn and went spiraling into a pit of momentary lunacy, in which reason and logic are overpowered by an irrational yearning to return to a reality that no longer exists.

When Markoff was charged with murder, for example, the 25-year-old told the Boston Herald: “I will stand by Philip as I know he is innocent. I love him now and always will.”

When police suspected a connection between the murder and two other robberies from hotel rooms in Boston and Rhode Island, McAllister told the Herald he was “intelligent, loyal and the best fiancé a woman could ask for.”

Their wedding was called off, but there was clearly no shortage of praise.

Then it was revealed Markoff hid 16 pairs of underwear under the bed they shared — mementos, police said, from the victims. Those were found along with a gun, believed to be the one used to kill Brisman, and about 60 pairs of flex-cuff restraints.

The gushing statements dwindled.

A strange thing happens to a mind when it is jolted awake from a long slumber of lies. For some frenzied period, it can render a person blind to the scathing truth.

It is a self-defense mechanism, no doubt — one intended to keep a person from emotional obliteration — but yields more productive results after it fades and gives way to sound reasoning and common sense.

Two weeks after Markoff was charged with murder, McAllister’s lawyer Robert Honecker Jr. announced that she is “moving on with her life,” sans Markoff.