It is important to remember his intent. Captain Hook’s intent for all these centuries has been to kill Rumpelstiltskin, and so far nothing has come close to making him want to stop. Even with his fondness for Emma, he still does not forget his plans. 🙂
He teamed up with Emma at first because she proved to be cunning, strong, and resourceful. But when she chained him up, she proved that not only did she not trust him, she refused to work with him. 🙂 Granted, she instructed the giant to let him go, but it would have prevented him from his revenge.
And then Cora claims that she will not take him with her to Storybrooke–she will deny him his chance for vengeance. This is something that he has been planning for too long to let go. 🙂 And so he does whatever he can do to get back onto his plans.
His actions are very similar to Rumpelstiltskin and Regina–though theirs are still much worse.