S-F-L-S

It means, Strangers to Friends to Lovers to Strangers.

"From Strangers to Friends, friends into Lovers and Strangers again." It is from the song Strange by Celeste, please go listen to it. It is absolutely beautiful.

"You know how relationship goes, s-f-l-s. Nothing ever lasts."
"S-F-L-S, we are in the love part right now, so I have to ready for us being strangers again."

S-F-L-S

FROM STRANGER TO FRIENDS, FRIENDS INTO LOVERS, AND STRANGER AGAIN.

friend 1 "Well you know how my relationship goes, s-f-l-s."
friend 2 "GOD! you're pathetic."