Sex with 'small' yours truly upset couples (5)
I believe the answer is:
items
'couples' is the definition.
(a couple might be called an 'item')
'sex with small yours truly upset' is the wordplay.
'sex' becomes 'it' (a common euphemism).
'with' is a charade indicator (letters next to each other).
'small' becomes 's' (abbreviation - e.g. clothes size).
'yours truly' becomes 'me'.
'upset' says the letters should be written backwards.
's'+'me'='sme'
'sme' reversed gives 'ems'.
'it'+'ems'='ITEMS'
(Other definitions for items that I've seen before include "Separate objects or units" , "Agenda points" , "Times (anag.)" , "Smite (anag)" , "Objects on a list" .)