Old lovers' agreement ignores right to speak honestly (4,2)
I believe the answer is:
open up
'speak honestly' is the definition.
'open up' can be an answer for 'speak' (opening up is a kind of speaking). I am unsure of the 'honestly' bit.
'old lovers' agreement ignores right' is the wordplay.
'old lovers'' becomes 'o' (I can't justify this - if you can you should give a lot more credence to this answer).
'agreement' becomes 'pre nup' (prenuptial agreement).
'ignores' is a deletion indicator.
'right' becomes 'r' (abbreviation).
'prenup' with 'r' taken out is 'penup'.
'o'+'penup'='OPEN UP'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for open up that I've seen before include "Start firing - speak freely - accelerate" , "Talk more freely" , "Become less secretive, or unlock door" , "Speak freely and without restraint" , "Begin to take shots" .)