Snowbaz

Simon Snow and Tyrannus Basilton Pitch. Canon slash. From Rainbow Rowell's Fangirl and Carry On.

Supposed to be each other's nemesis.

Baz had a crush on Simon since he was twelve, fell in love with him at fifteen.

Simon was basically obsessed with Baz without realizing it since age thirteen. (Somebody check this up)

Finally got together at eighteen. (Carry On, chapter 63/4)