A theologian once said that angels are constructs of love and holy rage, and chained to obedience through both. Or maybe a theologian hadn't said that. Maybe it was the Bright One himself, or just Uriel being grumpy.
But Bucky knows that he loves Steve, and he loves his taskmaster of a boss even as he gripes about him over beers after work, and he loves the dames with their red, red lips and smooth, soft curves (and he loves the guys, loves their strength and the tall, proud lines of them), and he loves old Mrs. Greene even when her rheumatism acts up and she turns mean as a wet cat. But he loves Steve most of all, and if Bucky is shackled to mindless obedience because of it, he calls it a good trade, because Steven Grant Rogers is the best person he knows. When it comes down to it, he figures his desire only adds a new dimension to a love that was already there, glowing hot enough to burn.
He was sent to Earth in a cage of mortal flesh to watch over Steve, and Bucky can do no less than love him with all his heart.