Now and then, during poetic evening, gets extremely mushy about love (5,2,5)
I believe the answer is:
every so often
'now and then' is the definition.
(I've seen this before)
'during poetic evening gets extremely mushy about love' is the wordplay.
'during' is an insertion indicator.
'poetic evening' becomes 'een' (e'en is a literary contraction of 'evening').
'gets' means one lot of letters goes inside another (gets can mean captures or absorbs).
'extremely' becomes 'very' (I've seen this before).
'mushy about love' becomes 'sooft' (I can't justify this - if you can you should give a lot more credence to this answer).
'een' going around 'very' is 'everyen'.
'everyen' enclosing 'sooft' is 'EVERY SO OFTEN'.
(Other definitions for every so often that I've seen before include "Occasionally" , "At intervals" .)