Hey Luke, sorry you had to sit through that. There are four endings, and six ways to get there. This is determined by two factors: your choice at the end of act 1 (agree with Argos' plan, deceive him, or make no promises), and whether you act abusive towards Argos and Asterion throughout the ruthless route's content. If you act abusive enough, you'll always end up on Dust and Silence, just through three different means. If you don't, you'll get the other three endings depending on your choice at the end of act 1.
*edit: don't feel compelled to keep going for the sake of an achievement. If this is content that distresses you, it's completely optional.