Check declaration of love for Cupid, possibly (8)
I believe the answer is:
observer
'cupid possibly' is the definition.
(I know that Eros is a fertility deity)
'check declaration of love' is the wordplay.
'check' becomes 'observe' (observing is a kind of checking).
'declaration of love' becomes 'r' (I can't justify this - if you can you should believe this answer much more).
'observe'+'r'='OBSERVER'
'for' is the link.
Can you help me to learn more?
(Other definitions for observer that I've seen before include "Non-participant; a paper" , "organ on Sunday" , "One watching attentively" , "Watcher, spectator" , "I notice" .)