Inara hates - absolutely - making promises she can't keep. Sometimes she has to change her schedule around in order to uphold her reputation and standing: she can't always be where she said she would be, but she travels with a band of thieves; she expects glitches.
The one thing she had not expected was Malcolm Reynolds, the cocky bastard. Oh, she'd picked up on the Latin long before the Tam girl had vocalized it! Mal, bad; why'd he pick that moniker? But she supposes it fits. "I will not service your crew," she'd said bluntly on their first meeting, and she'd meant it. She and Kaylee had spent some quality time together, brushing and braiding each other's hair and talking about glamorous city life - but other than that, Inara keeps her rituals separate, packed away in her shuttle behind closed doors. No problem.
The captain never knocks before barging in; never bothers to make sure she's decent. She rather suspects he's hoping to catch her in some state of undress one of these times. He is a callous, sarcastic, untrusting man, and she loves him.
She. Loves him. Him! Love! The thought had occurred to her one quiet night, when she'd lain in bed gently running her hands over the soft skin of her calves, hips, breasts, between her thighs, over and over until she gasped his name once and wondered why she suddenly wanted his hands.
Shepherd Book stands when she enters a room. The doctor defers to her only slightly, stiffly, and she knows it signifies whatever level of respect he can drudge up. Wash gets tongue-tied and stares at the floor or at his wife, and even Jayne watches his language when she's around. But Mal can't be bothered with any of it. Calls her a whore. No manners.
She doesn't understand, therefore, why she's kneeling in front of him and his eyes are squeezed shut and he's whispering please, please. Please? She holds one of his hands between hers; the other rests on the top of her head. Such strength in those fingers. Blunt and oddly tender. He caresses her hand, strokes her hair, falls back on her bed when she's finished, and breathes.
Inara really hates it when she has to break promises - especially ones she makes to herself.