A lot of debate that surrounds Attack on Titan is whether Eren is a good guy or an evil one. There is a difference of opinion among anime watchers on whether Eren has flipped the switch for the wrong side or whether he is still loyal to his country of Paradis Island. This is a question that is definitely hard to answer for anime watchers but there are many clues that suggest the development of Eren's psyche. He starts off with a mission to save humanity from the monsters called Titans but the more he fights, he is led to the realization that the Titans are simply a by-product of humans. He realizes that the fight was all along against humans, not monsters.

This is a pivotal point for Eren because this is where the fight for humanity changes into the fight for freedom. From being something that was for the collective good of people, it changed into a personal problem of a small island. This realization crushes Eren who is shouldering the hope for Paradis Island. Everything he believed up until now was not the actual truth. This is why we see Eren in Season 4 leaving the Survey Corps to reflect on the countless Eldians he had killed.

As the season progresses, we see Eren abandoning Mikasa and Armin, he chooses to act against the Survey Corps and creates the Yeagerists. He meets with Zeke and chooses to create the aforementioned group. What’s important to note is the reiteration that Eren shoulders the weight of the freedom of the Eldian Empire. He has seen what happens when he fights for humanity—countless lives are lost on both sides. This is why we believe that Eren chose to leave the Survey Corps. This is why there are signs that point out that Eren could possibly still be the good guy, as relative as the term is in such a world. The scene where he takes the shirt from the Yeagerists is merely a symbol that he is shouldering the weight of Paradis Island’s freedom and that he will give that freedom to them, even if he has to do it all alone.