FB = "FuckBuddy" = some may say "play partner" - a partner for sex (or BDSM play) that doesn't involve any other real attachment (for me, this means don't call or contact me between getting together times.)
FWB = "Friend-With-Benefits" = some may say "lover-friend" - a friendship that involves sexy times, but where the friendship is over-riding (and, for me, would exist whether or not there were sexy times) - hmmm? more than a friend and not quite a girl/boyfriend
I don't know that it is "cool" (or good/bad). It's how I am. And you are how you are...we are all our own individual persons. For me...I can enjoy sex without love (i.e. emotional attachment), I can also enjoy love without sex. These are two different things for me. Sometimes they intersect - and that is good. Sometimes they don't - and that is fine too. (To be quite fair, my life is full of both - love and sex - I have all that I need and more - all the extra is just gravy! )