Somehow routinely gel with setter I know only too well (5,7,2)
I believe the answer is:
youre telling me
'i know only too well' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'somehow routinely gel with setter' is the wordplay.
'somehow' is an anagram indicator.
'with' says to put letters next to each other.
'setter' becomes 'me' (the setter of the clue).
'routinely'+'gel'='routinelygel'
'routinelygel' anagrammed gives 'youretelling'.
'youretelling'+'me'='YOURE TELLING ME'
Can you help me to learn more?
(Other definitions for youre telling me that I've seen before include "agree entirely" , "I couldn't agree more" , "I am getting your message" , "Solver's instructing setter" , "I should say so!" .)