Looked up the dictionary. It says flow back. Does it mean "come back" here?
It is an agony that people here are beginning to get used to as time drags on and optimism and hope ebb away. (source)
It says flow back. Does it mean "come back" here?
Flow back, as like "go back", not "come back". Another synonym for these words is "recede".Let's look at the meaning the upper paragraph tries to demonstrate.
While some of the relatives will keep the fire of hope burning, there is the developing, devastating realisation for others that their loved ones will not be found alive.
What does this mean? It means that for instance when Mr.X and Mrs.Y found out that their son's plane has crashed, their relatives gave them hope that he will be found alive. However, as time passes, and as bad pieces of news come out they realise that they had false hopes.
Then the writer admits that it's really suffering to see how this hope is "fading away", or as the context puts it, "ebbing away". Hope I've helped.
No, "ebb" is used to mean that something is fading away. Here, it means that people started out being optimistic and hopeful (that some of the passengers might be alive), but they're losing hope as time goes by.