Like anyone is surprised that he's gonna keep the Endymion. He doesn't want to find the holy sword so he's not technically breaking the promise of returning it when he finds said holy sword, and if it's not as powerful as the holy sword then he might actually be able to keep it.
Plus when it's clear that the entire world is basically a simulation made by gods that are garbage, with multiple heroes running it at the same time, why should you care after you were treated like trash the first play through?