I get the feeling they've been hinting that in his "past" (aka the future he's prepping for) He and Romantica were together. They've placed way too much emphasis on her death and how it afected him. Also, the way he always reacts around her, especially when its about other girls.
All that said, I'm also getting the strong feeling that Adjest will still be endgame
Pay attention here because this is why AdjestxDesir was a thing to begin with. That magic swordswoman genius is a label that everyone but Adjest uses, when Desir approached her and told her that she was "good", but "nothing special" compared to what she can become when combined with effort and experience is when she found the crack in the wall everyone build around her, because Desir saw her as equal, not like in status, but equal as beings striving to better themselves.
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Neither Romantica is just a Hot-headed whiny, nor Adjest is just a genius kuudere. They're liked both because they're actually more complex than that while still being consistent with their own characters and motivations.
does desir end up w romantica or the blonde one... cos if its the blond one imma be so mad