That ending sucked. Here's a better one.
Kissing his dismembered head? Unbelievable... Good thing she's an idiot.
"MIKASA LOOK OUT!"
Ymir sees the the source of their power squirm quickly towards Eren, having already entered his titan's mouth.
With that Eren was able to regain his godlike power and finish his 'freedom'. He did this because, with his godlike power, he was able to see into the future that no peaceful resolution between Eldia and Marley could ever be made, including Zeke's plan. So that is why he choose to do this.
Fin.