I did an entire playthrough and chose that option still got the bad ending. Is there another requirement I'm missing? I have a stat in each element. My primary personality scores are straightfoward and manipulative.
Spoilers Below
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In order to get the good ending, I choose the easy route, had all three love interests war effort at 150, Emrys affection maxed, darkness and wood at 200. I also had zero suspicion and selected to work with the Alchemist's which gave me access to more information. The Garrison, the Mages, and the Alchemists all had approval above 100 as well. Like said in another comment I choose 'i don't know' when Emrys and you speak about the Sval.
Then after discovering the secret library I choose 'take the evidence and hope to use it to leverage for peace'. I hope this makes sense and helps !! I was stuck for a while but this is what helped me actually get the romantic ending lol