Everything is building towards something in the Flash Sideways by LockeIsTheKey

Every season we have gotten something different from the flashes. In the Season 1 flashbacks, we saw why the Losties were in Australia and a little about their background. In the Season 2 flashbacks, we got more background on the Losties. In the Season 3 flashbacks, we learned more about the Losties, but also about the Tailies and the Others. In Season 4 we learned about what happened after they left. In Season 5 we learned how they got back to the island. In Season 6, presumably we're learning what their lives would be like if the island had sunk after the bomb had gone off.

The common theme with each season's flashes are that they're building towards something. Season 1's flashes build towards them getting on the plane and the plane taking off. Season 2's flashes show major events in our characters lives that lead to them being in Australia (Jack ratting out his father which causes his father to go to Australia). Season 3's flashes again show major events that are major influences on the character's attitudes/views which in turn lead to them doing (Hurley's dad tells him having hope isn't stupid or whatever which leads to him fixing the van). Season 4's flashes build towards them realizing they have to go back and how they're going to go back. Season 5's flashes culminate with them back to the island. So if every season's flashes build towards something, what is Season 6's flashes building towards?

So far we've seen Desmond try and get everyone together that is supposed to be together (Hurley/Libby, Lock/Jack, etc.), but why is he doing that? What is the end game?

In my opinion, the universe is "course-correcting" through Desmond the way it did in Season 3. Nothing in the Alternate Universe was supposed to happen. Things were supposed to happen just like they did happen: Desmond comes to the island, O-815 crashes, etc. The bomb changed the future and now the universe is trying to fix it as best it can, using Desmond, by bringing the people together who are together in the original timeline. Once they are together, I think something is going to happen in the Alternate Timeline to split the relationships that are split in the Original Timeline (Hurley/Libby, Sawyer/Juliet, etc.). We have already seen evidence of this where Sayid and Nadia could not be together because Sayid had to leave (they could not be together in the Original Timeline). I think we'll find out that Jack and Juliet were once married and are now split, just like how they were briefly together on the island and then split.

The characters won't end up in the same physical situations in the Alternate Timeline, but they will be in the same mental states in my opinion. And maybe if we see Jack save Locke in the Alternate Timeline (assuming Locke takes his help), could that mean Jack will in some way "save" Flocke in the original timeline?