There were a lot of CMOHs between Sydney and Jack. The first big one came in just the second episode. The episode opens with Sydney slapping Jack in the face, and telling him to never speak to her again, because he knew Sloane was going to kill Danny before it happened. Later Will informs her that he discovered a plane ticket in Danny's name for the night he died. Sydney then meets with Jack and he confirms what she suspected: that Jack had purchased the ticket and tried to save Danny's life. It's the first time we understand that, however cold and distant Jack might often be, it is not just her safety that matters to him, but also her happiness.