Break down in tears initially: see, I'm upset (7)
I believe the answer is:
itemise
'break down' is the definition.
(I've seen this before)
'in tears initially see i'm upset' is the wordplay.
'initially' suggests taking the first letters.
'upset' indicates an anagram.
The initial letters of 'in tears' is 'it'.
'see'+'im'='seeim'
'seeim' is an anagram of 'emise'.
'it'+'emise'='ITEMISE'
(Other definitions for itemise that I've seen before include "List exhaustively" , "Read off list of things one by one" , "Formulate a list" , "List out singly" , "List one by one (S, not Z)" .)