Anime-only spoilers for what Roy did in Ishbal. And, oh yeah, I don't own FMA (though I'd give just about anything for Ran Fan).
Unforgiven
He has a picture of her in the bottom drawer of his desk, hidden away beneath stacks of military-issue stationary (addressed to a dozen different people, mostly her, and never sent), a pair of worn and blood-stained gloves, and a silver pistol given to him when he was promoted after Ishbal. There is a lock on this drawer, and he has long since stopped wearing the key on a chain around his neck--he doesn't need to be able to open the drawer in order to remember what is inside it with perfectly accurate detail.
The frame is of dark wood, with even darker red-brown stains where the blood refused to come completely out. There is a little blood beneath the glass, too, forming a dry, crimson crust over the photograph. It's an old picture, he knows. Old enough to be horribly inaccurate, but not old enough that you wouldn't be able to tell who the figure within it was, if you happened to know her. He did. Not well, of course, because he had the sneaking feeling that she would never forgive him, that she would always harbor a little spark of hatred for him deep within her heart, and that she'd already disliked him for keeping her best friends away from her so often and for so long.
Still, he is perfectly respectful when he addresses her. He calls her "Miss", extends his hand to her (she's taken it only a few times, long before she knew his dirty little secret, and now pointedly ignores it and him whenever she has the opportunity), and offers to arrange the appropriate accomidations for her whenever she's in town.
Except, she comes less and less often now. He hasn't seen her in more than a handful of months, and only really knows that she's still alive, even, because his closest subordinate is in almost constant contact with her. When he sees his second-in-command drafting a personal letter (and he can tell that it isn't for business because she doesn't use that hard, impersonal military paper, and because she only ever writes them when she's alone with him, in their home, entirely removed from the office), he asks her politely to wish the other woman (was she really that old already, it seemed like only yesterday that she'd...--) the best of luck with her business and with her health.
She only looks up from her letter-writing, fixes him with that soft, warm look that is reserved only for him, and scribbles his message on the bottom of her note in perfectly neat, elegant cursive. When none of the letters she receives bear a similar pleasantry, neither of them are surprised. Hurt, perhaps, but not surprised, and he tries to pretend it doesn't bother him, even when his most trusted employee (partner, wife, lover, conspirator) leans over to embrace him and there is the sparkle of a metal key on a silver chain hidden beneath her blouse.
Roy Mustang has a picture of her in the bottom drawer of his desk, hidden away beneath stacks of military-issue stationary (addressed mostly to her, and never sent), a pair of worn and blood-stained gloves, and the silver pistol he was given because he killed two doctors in cold blood, and left their daughter an orphan.
He can't blame Winry Rockbell for hating him.
End.
Give me some love? Or hate?