@icekatze Judging by the tone of the story, it's clear Joker doesn't have any ill will against the queen until AFTER he falls in love, so I don't think it's likely he will be a traitor (or the original culprit of the curse) for two reasons: one, Eleanor goes to him for help (and is more worried about his relations from the future, not what they are currently), and two, the story seems to set him up as male lead #1 (or the other leads would have been introduced earlier, in my opinion).
That aside: Considering everything, if you were the joker and aware of living in a simulation/game, you might play (mostly) by the game rules for the sake of survival (idk, there's probably a bunch of death flags he might want to avoid, such as being killed by the other male leads), so it's even possible he doesn't actually fall for the otome protagonist but does so out of necessity (in that case this implies he becomes aware of the possible death flags somehow, or is aware of what actions are necessary to avoid death flags). In this theoretical situation, the Joker would be willing to ally with Eleanor to avoid the death flags he is aware of (but why would he not be aware of the queen's death flags, or at least the possible futures where he "falls in love"?
Not only that, but Eleanor seems quite convinced by that specific game ending that Joker really falls in love, in which case I'm reading too much into Joker' planning.
Finally: what if the Joker originally gets with the queen and they break up in the otome game (followed by Alicia being otome protag BS)? That would perfectly explain Eleanor's extreme fears of any lasting relations with Joker, as well as her attitude of being completely sure the Joker falls for Alicia.