I read this a long time ago and have no luck finding it

if I remember correctly it is a side story in a volume connected to the another story as it is the same family.

Seme and uke a both students
Not so sure but from what I seem to remember they may like each other or is onesided.
If I remembered right they go to the seme's brother for help for sex or seme walks into room seeing the uke with the brother on bed (not quite sure)
The brother helps show them holding the uke open for seme to see. Seme may have thought uke was pure or something and afraid to go further before seeing this(??)

who needs drugs when you got yaoi