#alternatively...

he throws his hair up into a messy bun when he eats, and while he's sitting in the backyard reading, and when he comes to plop down on the recliner across from where you and your friend are sitting on the couch. he doesn't constantly speak during movies or shows, but he does allow himself to get immersed in the story. watching whatever it is intently and reacting to it as if he were walking alongside the story beats with the characters. he gasps softly when the leading man pulls the girl into their first kiss, he averts his eyes a bit when a shortlived sex scene occurs on screen (only to be teased by his younger sister about it), and even though he doesn't look like he'll cry at the sad scenes, he does give you tissues when you cry and offers hugs for when the tears won't stop. he rolls his eyes when his sister asks where her hug is and pulls her into the hug as well.

when he comes down the stairs dressed for work with his hair down and his button-down shirt and fitted slacks on, he smiles when you wolf whistle at him, and plays along when his family comments about how "dapper" he looks. he finds himself thinking of you in little moments when he's alone, be it at work or in his own home. maybe because you've become a small part of his almost daily routine (since you practically live in their home it feels like for the duration of the break, since his mom had insisted you stay with them instead of a hotel), or maybe because of something more. he notices your attempts not to stare, and finds it cute.

he wonders if you notice his tiny glances back, or how he touches your back when he moves around you in his kitchen, or how he sticks around the house more while you're there (in opposition to his sister saying her big brother is 'literally never home'). he would begin to ask you out for things: like... "hey, i want a new piercing, wanna come?" or "sis is sick, can you come with me to the pharmacy?" or "i think i need new work clothes, wanna go?" and eventually that would turn into dates, which turns into more.

your friend would be happy, eventually, that she could have you as a sibling in law, not just a friend one day once you two eventually start dating, and his family would be all for it.