3. Endgame choice. Enough has been said about his entire character falling apart the moment we choose Orpheus, it's appalling and completely out of damn character. And most frustrating of all? He can't be stopped. You can't toss a damn spear in the portal he goes through in hopes that maybe he gets hit? Not a chance to talk him out of it? "You choose Orpheus? KKTHXBYE" like what is this writing?
I can answer this one. His entire purpose is survival. Guess what he's not going to do when Orpheus is released? That's right, be allowed to live. So to him, it's better to cast his lot with the Netherbrain in hopes of getting another chance to free himself in the future. He's not looking to be a martyr or serve the greater good. He's in it for himself and you and your party members are just a means to an end. He doesn't even have a soul.