Regina did let go, but it was with some reluctance. If she didn't, she'd kill him, beat him to death, splatter his brains on his own wall - she knew that. And she had done some terrible things before, had killed people for less of a reason than she had to kill Hook right now (and oh, leaving her to be tortured without her magic was definitely a damn good reason), but there was something preventing her from doing it.
My life will be empty...revenge may sate your being, but don't misunderstand me, my dear. It's an end, not a beginning.
She saw the fatigue in his eyes, churning there like dark water; it was dragging him under. Her too, but it was a slower process. Regina hadn't had as much time to accept that once she got her revenge against Snow White, she'd be alone - she maybe knew it, in the back of her mind, but it wasn't something she had accepted. And she thought Hook had, but he was from a time before her and maybe he still had to go through what he did to realize that he was just a broken doll, and so was she - so was Regina - and no one wanted to play with the broken dolls, did they? Not for very long.
When her eyes locked with his, the anger in hers died down for a very brief second. But that was the only glimpse he'd get of Regina herself, and not the Evil Queen. "Pathetic," she spat, literally, on him and then turned to show herself out - causing a few crashes and bangs along the way, with more flicks of her wrist, to completely destroy his living room as a reminder of what would happen if he didn't decide to start playing by her rules.