bbl stands for "BE BACK LATER" it´s often used when you don´t want to type: Be back later, some people says it means: Big Ben London, but the original shortening is "Be Back Later" thats what it means.
Well i got to go bbl, bye.
Hey, want to grab a cheeseburger? No thanks, i have to run bbl ,see you.
"Bro" stands for Brother but can be used when you talk to for example a friend, it´s being used a lot in America.