Crying over? That is the wrong way to keep in step! (6)
I believe the answer is:
rueing
'crying over?' is the definition.
(to rue something is to regret it)
'that is the wrong way to keep in step' is the wordplay.
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'the wrong way' is a reversal indicator.
'to keep in' is an insertion indicator.
'step' becomes 'rung' (I've seen this in another clue).
'ie' reversed gives 'ei'.
'ei' placed within 'rung' is 'RUEING'.
(Other definitions for rueing that I've seen before include "Feeling regret" , "Bitterly regretting (longer spelling)" , "Feeling sorry for" .)