Eugeo's Weak Mind

When Eugeo gives in to the Pontifex's false proclamations of endless love for him to receive, it is shocking to see him fall so easily. However, his background growing up helps explain why he caves in without resistance. 

Eugeo is shown a fraction of a memory of his childhood with Kirito and Alice. Growing up with Kirito is blocked from Eugeo's and Kirito's memories, and these are the ones made as Kirito dives from the STL before being poisoned. Kirito is not supposed to remember their moments together. Eugeo sees Kirito and Alice in the woods, and they are speaking of their worries of being caught by Eugeo. At a glance, it appears that they are spending time together without Eugeo because they do not want him around. This is not the truth, though, and Kirito and Alice are actually making a small wooden sword as a present for Eugeo's birthday. Later on, Eugeo is able to see the whole memory. This is long after he fails to fight against the Pontifex when he first relives it. She controls him with her words saying that love is meant to be received, that this  love that is all for him. She inserts a Piety Module into his head, synthesizes him into an Integrity Knight, and sends him after Kirito and Alice. Eugeo has the module put in too quickly, however, and he ends up realizing what he has done to his dear friends. When the Pontifex goes to remove the Piety Module and place it in properly, Eugeo fights back in the fraction of time where he becomes himself again. At the end of the battle with the Pontifex alongside Kirito and Alice, Eugeo explains what love truly means. He is taught this by Alice Zuberg, and to him, love is something you give, not something that you get. 

Growing up, Eugeo did not receive the most attention in his home. He had multiple other older siblings that received more praise than him. After all, he had the calling of chipping away at the Gigas Cedar for the rest of his life. This is why Eugeo stuck to himself after Alice was taken away. The Pontifex uses this to her advantage to trick him into believing he would be recognized all on his own, that he would receive love meant for him alone. In the end, Eugeo overcomes this and realized love's actual meaning, even if this came to him just before he died.