Dogs of the Military
Hawkeye wasn't in love with her Colonel. To say such would imply that she chafed at being only his Lieutenant, that she wanted to hold him in her bed and kiss him and spend her days saying silly things to him. No, what she felt for him was far more degrading to admit to, and yet perfectly natural.
Total and utter devotion. Loyalty without the restraint of self-preservation. Something rarer, and ultimately more powerful, than any insipid love poem could hope to be.
Hawkeye was loyal to her leader. Loyal to the point of dying for him, to making others die for him, loyal as only a Lieutenant can be loyal to a Colonel, their bond forged uniquely by the simultaneous rigid constraints of rank and the forced intimacy of war.
They had started out crammed into some grimy little space in a rebellious city with Hawkeye trying to get a lock on some fat little commander and Mustang frying anyone who tried to sneak up on them. Afterwards they had sat together, soaked in others' blood, and drunk out of chipped cups to the crackles of their radio, drunk until they had quieted long silenced screams.
She had listened to his still evolving ramblings about becoming top dog, taking control, and making the world a better place. For him and 'his' people, if not for anyone else.
"Will you follow me?" He had asked for the first time, the slur in his voice indicating he might not remember her answer tomorrow.
"Yes sir." She had replied anyway, and felt her resolve burn bright.
As alchemists are dogs of the state, so too are the footmen they employ. They are trained and collared, and when needs must the dogs of war are unleashed to wreck havoc upon the populace. However much people like Mustang admire their loyalty in the face of abuse, they still have teeth and claws that must be used.
Winry would say it's sad, that the cold hawk cannot love. Edward would say it's inconceivable how someone as stupid as the Colonel manages to inspire such devotion. And Roy... he would say nothing, because it was only what he expected of her: to guard him through the night, to protect him when she could, and to love him in what she would say was an utterly sexless manner. And in return he too would love her, in his own way, a way he wouldn't claim entirely sexless because hey: he was Roy Mustang and he had a carefully crafted image to maintain, but sexless enough to hold her whilst she bled, and curse her when she failed.
"Idiot! Why did you do that?" He shouted, sweat shifting the dried blood on his face as he carried her out of the ditch she had been flung into. The attack had been designed for him, but it was no use telling 1st Lieutenant Hawkeye to let the enemy have their way when her Colonel was involved.
"Dogs are stupid, remember?" She told him, and no more words were needed.