Should I weep in the fifth month, separating myself? - “In the fifth month,” from the seventh to the tenth day, Jerusalem was in flames, fired by Nebuchadnezzar. “He burnt the house of the Lord, and the king’s house, and all the houses of Jerusalem and every great man’s house he burnt with fire” .
Jerome: “Now since it is said that the temple is builded and we see that no cause of sorrow remaineth, answer, we pray, are we to do this or to change our sorrow into joy?”
Separating myself - This seems to be added, to intensify the fast which they had kept. The Nazarite was bound to “separate himself from wine and strong drink” Numbers 6:3, and so, they severed themselves to the Lord, and consecrated themselves to Him (Numbers 5. See the note at Amos 2:11). These had severed themselves from food, from things pleasant, from pleasure, from sin, it may be, for the day, but not abidingly: they had not given themselves to God.
As I have done these so many years - Literally, “how many.” As if, although they knew that they were seventy years, they could not count them.