I think that when they all go back to save Jack as we all know they will... Kate is going to get an eye full of Jack "fitting in" with the others and possibly how "close" Juliet and he have become and that will throw her back in the arms of Sawyer... She is going to have to deal with that the way Jack had to deal with, Kate & Sawyer's Cage Lovin.... I feel Jack is not forgiving when it comes to his heart.. Hes been hurt a lot from what I've seen...

__________________
Please don't give up, Des. Because all we really need to survive is one person who truly loves us. And you have her. I will wait for
you. Always. I love you, Pen

DESMOND: I love you, Penny. I've always loved you. I'm so sorry. I love you!
PENNY: I love you too.
DESMOND: I don't know where I am, but--
PENNY: I'll find you, Des--
DESMOND: --I promise--
PENNY: --no matter what--
DESMOND: --I'll come back to you--
PENNY: --I won't give up--
BOTH: I promise. I love you.