Bitterness of a pro abandoning riches (8)
I believe the answer is:
asperity
'bitterness' is the definition.
(asperity is bitterness or sharpness in one's tone)
'a pro abandoning riches' is the wordplay.
I cannot quite see how this works, but
'a' could be 'per' (eg 'one a day' means 'one per day') and 'per' is located in the answer.
This explanation may well be incorrect...
'of' acts as a link.
Can you help me to learn more?
(Other definitions for asperity that I've seen before include "Harshness, bitter coldness" , "Harshness of tone or manner" , "Roughness, harshness or coldness" , "Roughness, bitterness" , "Roughness of temper" .)