UPDATE: ERROR.
This guide follows the SFW base game ONLY. This is because the NSFW DLC CGs are not saved when you unlock them, and because the DLC prevents you from being able to unlock the 2nd and 15th (2nd to last) CGs with it installed.
I'm not sure why the DLC does this, but it does. If you want those 2 CGs and you don't want to compromise your experience with the NSFW patch - you can go through this guide as normal, then uninstall the DLC and play the "Elyon Good Ending" and the "Elyon/Yvoress True Ending" again - which will pop the last two.

As always with my guides, here are some things to keep in mind as you delve into the game:

• 2 of the 7 endings are closed off until you complete the game once. When you've finished it once, the choice will appear alongside where you would normally go to the whispers, or the screaming man. Note: This option still unlocks in old saves from your first playthrough, as if it's a new save.
  
  
• There are only 2 romance options - Yvoress and Elyon. Elyon has 3 endings, and Yvoress has two, for a total of 5, with another 2 endings in the "mystery" category where you aren't really romancing anybody.
  
  
• There are actually "dead ends" in this game. Following the guides will avoid them, but it's worth mentioning here that they do in fact exist - and are usually indicated by the narrator/Alfonso being confused about the scenario and asking you to go back and fix it.
  
  
• I personally recommend doing Elyon's route first, then Yvoress' and then the mystery route - as this is the order of the CG appearance, and sets up the world in the best way.

This route unlocks the achievement - "Elven Delight"

• Accept the offer
  
• A man screaming for help
  
• To give him mouth to mouth
  
• Take him back to the castle with him
  
• Offer Elyon the entire bread
  
• Stay hidden and watch from afar
  
• Distract the wolf for Elyon could get close
  
• See the town with Elyon
  
• At the docks - Alternatively, you can also go to the town plaza to unlock CG #3
  
• Offer an explanation
  
• To be understanding

This route/ending unlocks CGs #1, #2, (Potentially #3), #4 and #6.

Credit to Elphie for finding this route.

• Accept the offer
  
• A man screaming for help
  
• To pick him up and try to wake him up
  
• Take him back to the castle with him
  
• Either (I chose change the subject for new dialogue)
  
• Either (I chose to interrupt)
  
• Distract the wolf so Elyon could get close
  
• Head directly to the inn
  
• Either (I chose to offer an explanation)
  
• To be understanding

This route/ending unlocks CG #5.

• Accept the offer
  
• A man screaming for help
  
• To pick him up and try to wake him up
  
• Escort him back to his own kingdom
  
• Change the subject
  
• Interrupt Elyon
  
• Attacked the wolf
  
• Head directly to the inn
  
• Ignore the question

This route/ending does not unlock a new CG.

This ending unlocks the acheivement - "The Sorcerer and his Prince"

• Accept the offer
  
• Mysterious Whispers
  
• Faced the Sorceror
  
• Insist that Yvoress should do it
  
• To teach Yvoress how to use it
  
• Try to comfort him
  
• To go first
  
• Yvoress

This route unlocks CG #7, #8 and #10.

• Accept the offer
  
• Mysterious Whispers
  
• Ran for his life
  
• To go get dinner himself
  
• Interrogate Yvoress about his magic
  
• Try to go back to sleep
  
• To make Yvoress go first
  
• The Sword

This route unlocks CG #9.

This route cannot be accessed on a first play-through. You need to complete the game once with either Elyon or Yvoress.

This route unlocks the achievement - "Once and Future King"

• Two people arguing loudly
  
• Quickly offer his own lifeforce
  
• Keeping an eye on them
  
• Tell Yvoress and Elyon to come down
  
• Rest for a while and think about it
  
• Tell Yvoress and Elyon about the writer
  
• Go ahead and enjoy your happiness, Prince

This route/ending unlocks CGs #11, #12, #15 and #16

This route cannot be accessed without completing the game once first with either Elyon or Yvoress. It does not unlock the achievement for the true ending, despite ending with a similar world state.

• Two people arguing loudly
  
• Make Elyon share his lifeforce with Yvoress
  
• Leaving them alone for a moment
  
• Tell Yvoress and Elyon to come down
  
• Leave immediately
  
• Keep waiting for the court magician
  
• Escape the Dungeon
  
• Admit his own responsibility
  
• Go ahead and enjoy your happiness, prince.

This route unlocks CGs #13 and #14.