Having desires and acting upon them is the major deciding line. The princess and the country did absolutely fucked up shit before this. But the Saintess 100% pushed her over the edge. I don't think she would've killed his entire village, him, his sister, and everyone involved with him. If not for what the Saintess did. But, that doesn't make up for all of the other horrible terrible and downright awful things she's done. She is thoroughly a terrible princess. But the saintess triggered actions that are what made him realize what was going on.