Agree with an Eastender friend (5)
I believe the answer is:
tally
'agree' is the definition.
(I know that agree can be written as tally)
'with an eastender friend' is the wordplay.
'with' says to put letters next to each other.
'an eastender' becomes 't' (I can't explain this - if you can you should believe this answer much more).
'friend' becomes 'ally' (an ally is a friend or supporter).
't' put next to 'ally' is 'TALLY'.
Can you help me to learn more?
(Other definitions for tally that I've seen before include "Record; current score" , "Agree - count" , "Square" , "Reckoning of a debt or of votes" , "Score; correspond" .)