There are seven different endings: Revenge, Submission, Dominance, True Love, Manipulation, Blackmail, and Fairy Tale. Each ending has its own achievement (in the Extras menu). You can end the game in Act VII, VIII, or IX. Depending on how you end the game, you usually get a choice between several of the endings (but there will always be several endings blocked off by your decisions during the game). The only really "bad" ending is the Submission one, but it is hard to bring the game to a state where it is impossible to avoid it.
There is not just one way to reach each ending, though they all have some requirements. Depending on how you go through the game, some of these requirements will be met while others will not. The major decisions are how you deal with the prince in Act V, how you handle the conversation with the princess in Act VII (especially this one has a high variety of outcomes), and whether or not you flee the palace in Act VIII. But many of the smaller choices that you make also determine how the story will play out.
I don't know if a walkthrough has been posted. I wrote one for myself, but never posted it, mostly because I think the fun is in building your own story, and/or discovering all the things you can do in the game yourself (there is replayability as you cannot discover all the major content of the game with a single playthrough). But if you have questions I am happy to answer them.