i firmly believe kaeya had a crush on jean when he was a kid, at the very same time diluc did. however, diluc never voiced or admitted of his crush on her (and frankly, he didn't have to, as obvious as he was), but kaeya, obviously, noticed, and decided to keep in his brother's shadow and neither push him closer to jean (as to set him up with her, or create opportunities for them to get closer) nor try to turn him away from her. he decided it was more amusing to watch his older brother struggle on his own with his silly (and by god, rare) crush, never turning down an opportunity for amusement and bold teasing as he tried to get a verbal confession out of him. diluc eternally (and externally) remained in stage one: denial, while the internal truth leaped lively inside his heart. diluc was also most certainly a victim of provocations, such as 'if you don't give her this flower, i'll do it myself' which kaeya knew would pressure the redhead into actually doing it, and which resulted in diluc snatching said flower from his brother's hand and childishly speedwalking towards jean before kaeya could act upon his words (and gods knew he would if given the opportunity), leaving kaeya standing with a bittersweet smirk and childish jealousy on his face. kaeya never told anyone about his own crush, and hid it so well from the world as a treasure and a strange feeling that could never, yet could only ever belong to him. he hid it, sometimes even from himself, and forcefully suppressed it, as he felt he was in no place to harbor such emotions or take diluc's chances, so it eventually died out as everything else did. i don't think jean ever returned diluc's feelings - her view of him, i assume, was far too respectful and full of different kind of awe and admiration (especially during the knighthood days the three kids spent together), and so she always saw his acts and flirty attempts as mere acts of kindness and politeness, and him as a well-mannered boy. in contrast to kaeya's crush, everyone and their mother knew of diluc's 'secret' crush and crepus found it very amusing (he was against arranged marriage yet still entertained the idea of, in a way, uniting the two clans). he was fond of jean and pleased to know his son genuinely liked her. frederica certainly thought of the union and thought of diluc as a great option, tho i believe she always thought of kaeya as a more responsible brother and would let jean go anywhere as long as kaeya were there too. aside from his harmless troublemaking habits, i also believe she could see kaeya's outstanding intelligence and sense of reading people, situations and surroundings, as well as his constant caution much better than crepus could, so kaeya was, in a way, both a trustworthy friend and a safety measure for her daughter. he wasn't a second option for future arrangements though, he wasn't an option at all, for he was still an outsider in her eyes, a stranger, as good of a kid as he was. in any case, i also think kaeya had his moments with jean that differed from diluc's sweet (kaeya: you mean cringe) moments with her. so, as kaeya didn't necessarily try to get closer to her (as she could potentially be a lady reserved for the ragnvindr heir by blood - diluc), there were definitely very brief moments without diluc present in which kaeya tried to bond with jean the best he could without getting in his brother's way. but, being a kid that he was, he still wished, selfishly so, to satisfy his own heart's needs and cater to those strange emotions that confused him, even if he thought he had no right for it (my poor boy).