Feel bitter about fees regularly being included in lease (6)
I believe the answer is:
resent
'feel bitter' is the definition.
(I've seen this before)
'fees regularly being included in lease' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'being included in' is an insertion indicator.
'lease' becomes 'rent' ('rent' can be a synonym of 'lease').
The alternate letters of 'fees' are 'es'.
'es' put into 'rent' is 'RESENT'.
'about' is the link.
(Other definitions for resent that I've seen before include "Feel displeased or indignant about" , "Feel affronted by" , "Feel bitterness at (something)" , "Enters (anag)" , "Take offence at" .)