Thor: The Dark World (liveblog) [x]
In all fairness, you could maybe make a case that Loki may well have decided to help Thor because there wasn’t another way off of Svartalfheim without him. Calling for Heimdall wasn’t an option, because Loki was not Asgard’s favorite, at least Thor would protect him. (But it’s not actually true, because they still had that Asgardian skiff, we see that Loki got off the Realm and back to Asgard just fine.)
But he could have gone back for the skiff (there was no reason it wasn’t working, right? I assume Thor and Jane probably originally would have used it but they had to take shelter from the storm, then they realized the barriers were thin between the worlds there or, if worse came to worst, they could have called for Heimdall) and followed the pathways back out of there, Loki could have fucked off to anywhere he liked, so.
YOU WILL NOT TAKE THIS AWAY FROM ME, that Loki is not a good person, he doesn’t do good things just for the sake of doing good things. But there are a handful of people he cares about, that he does want to be emotionally invested in him, to still care about him, even as he fucks a lot of that up or pushes them away. And Thor is absolutely one of those people, Loki LOVES Thor, even if it’s mixed in with a lot of confused shit. He spends every scene between them constantly trying to draw some sort of reaction out of Thor, to get him invested in Loki again! He’s constantly jealous and obnoxious when Thor’s paying attention to someone else! He could have fucked off here and left, but instead he goes to help Thor in that fight.
You can argue that Loki was setting up a plot to make it seem like Kurse was going to kill him, so he could pretend to be dead so Asgard wouldn’t go looking for him, but the scene wasn’t shot with that in mind and I don’t buy that theory. I think this was entirely genuine on Loki’s part, because he will always love Thor (just as Thor will always love Loki, that we see both those things here), no matter that he’s pretty fucked up and confused and angry right now.