One thing to remeber about Jack is he has always been anit-fate, the opposite of locke. I think him seeing Ana was another holyshit moment for him, like the guy in the bunker. I think he is starting to realize that maybe they were all put on that island for a reason not just a bunch of coincidences.

I agree it was odd for Michael to not react, but there was a gap where he arrived, then they started to go out. He explained the situation to Jack, maybe they explained the bunker to him?

Next weeks episode is centered around Kate.