This sounds like the second couple of "Make me Bark." Except, the one having a crush on the big brother is the big brother's fiend
AHHHHH YES ITS THIS ONE, THANK U SMMMMM
Oop I got the wrong one (^ц^ )
it was "no secrets between us" but imma check this one out too cause i love this plot
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it was colored and about 2 best friends. basically, when they were kids, friend A found friend B jerking off to friend A's brother. friend B doesn't know friend A knows about his crush on friend A's brother so they continue being friends and a few years pass. they're now in high school and friend A decides he's going to help set friend B and his brother (who's now in college/working) up. a loooot of shit happens and friend A finds out that his brother knows about friend B's crush on him. he later tells friend B that he knows he's into his brother and friend B gets really madddd.
that's all i remember, sorry if it was confusing
i damn near had a stroke writing this