Uknighted Dream

Eugene and Stalyan were always meant to be doomed because they couldn't heal or get out of the toxic embiroment, Eugene needed someone who sees his true self while Stalyan needed someone who didn't left her or made her feel she is the other woman. That's why Rapunzel and Brock were meant to always be pair for Eugene and Stal, Rapunzel saw in Eugene a good person besides his thief mask while Brock never left Stalyan's side of made her feel she is the other woman.

Also i felt that if Stalyan ended up alone it wouldn't make sence because her arc is about that Eugene left her for Rapunzel and she became an antagonist, following her father's order as Let him poison Lance and agree that Eugene should marry her. Her arc was healing after she realize that she needed to change to be happy and then she apologize to Rapunzel and Eugene and go find her way but it wouldn't be a closer because she still deals with her abandoned trauma, that's why i think that the writters decides to put her and Brock together like it a close to her arc and also to his arc that someone sees him for he truly is.