This I feel like is a what-if story and what-is story. From my perspective, it seems that Eren is the one hurt and Levi is there to help but Eren has a what-if scenario where Levi gets hurt. Eren then realizes that he is glad that it is him, who carries the titan blood, is hurt and not Levi because Levi carries no titan blood and if hurt terribly, Levi might die.
This I feel like is a what-if story and what-is story.
From my perspective, it seems that Eren is the one hurt and Levi is there to help but Eren has a what-if scenario where Levi gets hurt. Eren then realizes that he is glad that it is him, who carries the titan blood, is hurt and not Levi because Levi carries no titan blood and if hurt terribly, Levi might die.