Bad feeling, as I'm taken in by a mate (8)
I believe the answer is:
acrimony
'bad feeling' is the definition.
(I've seen this before)
'i'm taken in by a mate' is the wordplay.
'taken in by' indicates putting letters inside.
'mate' becomes 'crony' (I've seen this before).
'a'+'crony'='acrony'
'im' placed into 'acrony' is 'ACRIMONY'.
'as' is the link.
(Other definitions for acrimony that I've seen before include "'Bitterness, acerbity (8)'" , "Bitterness, ill feeling" , "'Bitterness, sharpness (8)'" , "Acronym I coined in hostility" , "Bitterness or ill-feeling" .)