Not very popular opinion (I think?), but I don't think Shiro saw Keith as his brother before a long, long, long time, mainly because he wasn't sure if Keith cared about him as much as he did
idk I think shiro gave a lot to Keith, and he took him in loving him like he would love a brother but he never would've thought, by himself, "oh yes, that kid definitely sees me as his brother" so when, Keith finally tells Kuron "I love you, you're my brother" the reason why it comes as a shock is because well, Kuron has Shiro's memory, and he's surprised to see that the love Shiro has for Keith is returned
Shiro knew Keith cared about him a normal amount, but he never thought that Keith would consider him as family, yk? especially since Keith is very shy about his emotions I guess, so shiro just assumes that "yeah I guess Keith has to like me a little. he saved me cause I helped him get out of the foster system or smtg"
so when Keith DOES tell him he loves him & sees him like a brother (after an even longer time because the fight with the clone traumatized him) I think shiro lowkey. combusts
idk hahah I think about this a lot
