The problem is the words he said. >.> From her point of view it looks like this:

She saves a guy who promises her a ship to sail on if she frees him as well. She does so. Then halfway through the escape he suddenly runs off. She follows, angrily of course, and finds him again. She gives him one last chance to keep the promise he made (Call it a deal or promise, i don't care. He did promise.) but instead he uses this chance to clearly tell her he's backing out of his promise and betraying her. If Octavius was in her shoes he'd want to murder her too. >.> Not much a man of his word after all apparently.

I mean, these were his literal words: "I'll give you whatever the fuck you want. Anything! Don't you walk away from me, lass. I'll fucking kill you. I will. You can have anything you want, anything. Just get me out of here." No mention of a handshake or anything. Only a "just get me out of here." So yes, he really is going back on his promise. >.>