Kiss him madly? It's a belief (7)
I believe the answer is:
sikhism
'a belief' is the definition.
(I know that Sikhism is a type of faith)
'kiss him madly?' is the wordplay.
'madly?' indicates anagramming the letters (I've seen 'madly' mean this).
'kiss'+'him'='kisshim'
'kisshim' is an anagram of 'SIKHISM'.
'it's' is the link.
(Other definitions for sikhism that I've seen before include "Religion with gurus" , "Indian religion founded by Guru Nanak" , "Kiss him (Anag)" .)