FLANEUSE SAID:
I don't quite follow how and when Sarah & Ben meet and grow some kind of romantic interest in one another.
I don't know when exactly Sarah and Ben meet either. My theory is that Ben was manipulating Sarah, blackmailing her somehow, NOT that they were having a romantic/sexual affair...just their meetings were secret from Jack.
FLANEUSE SAID:
Also, I thought that Ben was somewhat able to leave the island and come back, before the explosion at Des' hatch took place. If that's the case, why bother with time-traveling to find yourself one Jack Shepperd to cure some future-cancer. As opposed to checking into a clinic in Florida or somewhere in Switzerland..
I was saying that Ben knew he would get a spinal tumor and that he would need someone to fix him in order for him to go on and protect the island from whatever danger it is he sees the freighter people posing. For that reason he might go to great lengths to ensure that Jack was on flight 815. If he was able to glimpse a possible future, he might have known that the end of Jack's marriage would put him on a certain path eventually ending up on the island, and therefore Ben would want to ensure that the marriage did end. I don't have it all worked out yet, but I like that there are loose ends that I can tie up with this theory.
My thought process must have been totally muddled in that post. Sorry!