i feel like i kinda answered this two places in my 1kr thread and in this rs answer

i think late 2019 is when felix stopped being "just" a little brother to chan. even just platonically, i think felix became someone more "equal" to chan in how their relationship was in terms of support.

"why couldn't have chn just kept looking at flx as a brother,..." well we don't know if he stopped? or if he ever really did? we often use words that aren't precise to describe how we feel bcs we don't have any others.

i don't think chan truly viewed felix as a little brother, like he does with his actual brother. but that is the how we learn to talk about those close relationships?

sorry gonna go on a little rant about the allotistic view of the world here:
- we live in a society that says the most important relationships in your life is: family and your romantic partner. that is the massage we get served. friendships are never really high lighted as something to actually prioritise or place the same value on. so what do you do when you have a friend you really truly value and have immense love for? -> you compare them to family because you can't compare them to a romantic partner, that's something else. strong platonic feelings are for family only. sometimes we gotta remember that people just don't have the right words to describe what they feel. rant over

i think felix being there to give him support changed him from someone that chan needs to solely protect to someone he can lean on. and that does a lot to shift how you view someone. being able to let himself be vulnerable felix also does a lot. so yeah i think late 2019 bcs chan let himself be taken care of is what truly opened his eyes.