kylo and cal might not be fast friends at first interaction, but cal has a way with people. he grows on them, every one of them. whether they want him to or not.
at first kylo reminds him of trilla in a bad way; a broken boy, lashing out in the pain of his circumstances, unable to see the forest for the trees of his trauma. however, just like trilla, cal feels the pull of the light in him strongest when he tries to deny it.
trilla's last words before her life was cut short a red saber held by none other than this petulant man's grandfather. but vengeance is not the jedi way, and cal is a jedi knight, he won't forget the responsibility cere laid on his shoulders. instead, he begins to train with kylo.
not under him, no, he's not a knight of ren. they are their own group, older and seperate from the first order. they have some history with kylo that cal can't touch; it goes beyond his present arrangement with them, something about his uncle and his flight to the first order- but that's for later.
no, but alongside him. and occasionally, over him. kylo ren is an avid, hungry student. he wants to learn, and he will accept knowledge from anywhere and at any price, from anything. a holochron, a series of cruel now-dead masters, or a living jedi knight serving his deadly rival. cal is surprised by the dedication kylo shows to learning new skills, and the focus he is capable of achieving in pursuit of perfection - focus that eludes him in other areas of his life.
they talk about this one night in the gym, while cal helps kylo spread bacta gel on the evening's bruises. (kylo has a lot more bulk to manage while attempting to run across vertical walls, and he falls a lot more often than 10 year old cal did.) kylo isn't, as cal had first assumed from his observed interactions with hux, a needlessly aggressive and obstinate idiot. in fact, without hux around, kylo is an insightful and remarkably level-headed man. it's an interesting dichotomy, one which reveals its source in a hot flash of clarity with cal's bare hands on kylo's shoulder.
the dance is as old as the galaxy, cal is just a new partner in the mix.
at first, he's not sure what to do with this information, if anything. does hux know about kylo's feelings for him, should cal tell him? not for the first time since this started, he feels torn, this time between his loyalty to hux and his loyalty to the man he has come to see as a student, reluctantly or not. he knows if he gives this information to hux carelessly and hux uses it callously, cal will lose his connection to kylo in the betrayal, and kylo will lose his connection, ever growing, to the light. and what about the hint of want for himself, however brief and quickly withdrawn? much to think about.