Mary cannot possibly be in love - and that's official (5)
I believe the answer is:
mayor
'official' is the definition.
(I have seen 'Municipal official' mean 'mayor' so perhaps 'official' could also mean 'mayor')
'mary cannot possibly be in love' is the wordplay.
I cannot quite see how this works, but
'love' could be 'o' (love means zero in tennis) and 'o' is present in the answer.
an anagram of 'mary' is 'mayr' which is present in the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'and that's' acts as a link.
Can you help me to learn more?
(Other definitions for mayor that I've seen before include "Municipal head" , "For example, Henchard" , "Chief magistrate" , "Local bigwig" , "Officer" .)