The Brief: BF is an abbreviation for boyfriend.

DEEP DIVE
Variations of the term include “soft bf.”
https://twitter.com/nobody_stop_me/status/1068217178472808449
Lil sum for my bf π happy birthday, I love you! β€οΈ pic.twitter.com/5lT1TYZBRC
— Eveβ₯ (@evelynpea_) November 29, 2018
Hey soft bf pic.twitter.com/ZWiuxySki1
— hannah (@lillseb) November 29, 2018