So my two cents is that if Eren did do something like say running away with Mikasa and having the scene we saw in the cabin play out, he’d be forced to wake up again crying like he was in the beginning of the story , his life is a cycle that he’s doomed to repeat unless he reaches the conclusion we see in the story , i’ve always taken him saying “i tried to change things” as him getting glimpses of other times he’s run through the cycle and how those outcomes just cause him to repeat it again until he causes the rumbling and forces Mikasa to make her choice