it means to follow me on social media or anything like that & the other word fb means follow back and fmb is the same thing as fb it’s just saying follow me back ..

To be dull, comatose, longwinded, unexciting

forever misunderstood

Fucking Magic:
1) The idea that something resolved itself; the idea that something resolved magically; Used as an answer when the truth may not be present
2) Shortened version of PFM; a miracle; low probability

FM's are a commonly used slang for fake money

Fm sometimes means "For me", "For my" and maybe even "Fuck me"
It's the way you read it makes sense