Most of the decisions made that affect the game ending are in Act 3 where NPCs will outright mention them. 4 of them are right at the end where you pick how you want to end the journey and affects the world with those decisions. These greatly affects how your companions will treat you (as some of them will state what choice they want and what choice they will hate) in the epilogue.
Most of the decisions in Act 1 and 2 affect the NPCs you used to talk to and how they decide to live at the end of the game, assuming they aren't dead. Just a few lines of narration.
Last edited by Ellezard; 27/09/17 08:56 PM.