logn before与before long用法有什么区别

long before时间状语或连词“很久以前,在……很久了”
e.g I haven't received your letter long before.我很久都没收到你的来信了.
It won't be long before we meet again.我们很快又可以再次见面了.
before long时间状语,相当于soon
e.g He will come to see us before long.

long before:很久以前
before long:不久以后