Written for Cordelia_V on her birthday
On The Theme of Infidelity
Everyone had expected it to be Harry.
After all, quite apart from having almost single-handedly saved the wizarding world from Voldemort's evil machinations, Harry was a good-looking, not altogether unintelligent young man with a glamourous job playing Seeker for the English National Quidditch team. It was natural to assume that there would be scores of women and men attracted to his celebrity...possibly even some who'd go so far as to offer to pay for the privilege of bedding him.
In the face of such temptation, who could honestly have blamed Harry for straying, particularly considering who he'd be straying from? Certainly not most of his friends and acquaintances.
However, while there was the occasional Quidditch groupie hanging about after games, and the odd grateful citizen (willing to show Harry that they could be very, very grateful indeed), Harry actually received far fewer propositions than anybody who'd been connected with the Order, apart from Mundungus Fletcher.
The reason for the apparent lack of interest was, it had to be said, largely due to the identity of Harry's ...
Despite being cleared by the Wizengamot of all war-related charges and lauded in the press for his service to the side of Light, Severus Snape's reputation was still...well, he'd killed Dumbledore, hadn't he? Who knew what he'd do to somebody who dared to flirt with his...
In any case, even if Snape's name alone hadn't been enough to strike fear in the hearts of anybody who might have tried to put the moves on the Boy Who Lived Again, Harry wouldn't have ever considered accepting anybody's advances.
You see, despite not knowing his parents - or maybe because he didn't know them - Harry idealized the love shared by James and Lily Potter, and he was determined to show the same love and loyalty toward his...
"Oh, fine! Sometimes you're so immature, Ron."
...toward the former Death Eater. 
In any case, everyone had expected it to be Harry who strayed first, but...
"Who's telling this story, Ron?"
"You, but you're ignoring the important parts."
"I suppose you could do better?"
So...Harry had been under Imperius or something for a six or seven years...
"Don't give me that look!"
"But you're being unfair."
"It's the only thing that could explain why he was with Snape."
All those years, and Harry hadn't even looked at anybody else. Of course he didn't, because he wasn't a cheating bastard like that prat he was living with. There was Harry, staying in all the time, while Snape was out with a different man every night of the week.
"Borrowed Witch Weekly from Mum, didn't I?"
Of course, the real question was who in their right mind would want to have anything to do with that ugly prick. Who did he think he was, swanning about at the clubs, out all hours, when he had someone at home who....
"Harry wasn't staying at home."
"He...what do you mean?"
"What about it?"
"You know Harry couldn't go out after the war, not like a normal person."
"So Professor Snape brewed Polyjuice and..."
"Are you telling me all those men Snape was with were really...Harry?"
And they lived happily ever after.
 If you have any complaints regarding the use of this unfortunate epithet, take it up with Ronald Weasley.