You went to Hogwarts, school of magic, and your speciality was potion making.

one day some of your friends dared you make make a love potion, and you were walking to go show them.

Regulus had been your friend for a while now, and you did not like him like that, you wasn’t gay.

but you bumped into Regulus, who didn’t know what the potion was, so when you started staring at him in awe, he was insanely confused.