best friend forever

Plural

best friends forever

someone's best friend, ‌used by young people on social media, especially in text messages

Despite living in different cities, Tom and James have remained BFFs for over a decade, talking on the phone every day.
Jenny considers her dog to be her BFF, as they do everything together and share an unbreakable bond.
After going through thick and thin together, Maria and Julia are more than just friends; they're BFFs who support each other through everything.
Even though they've only known each other for a short time, Jake feels like he's found a true BFF in his new roommate.
Mia and Sophie have matching necklaces engraved with "BFF" to symbolize their lifelong friendship.