We must be in a group - it's adorable (5)
I believe the answer is:
sweet
'adorable' is the definition.
(thesaurus)
'we must be in a group it's' is the wordplay.
'must be in' is an insertion indicator.
'a group' becomes 'se' (I am not sure about this - if you are sure you should believe this answer much more).
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'we' inserted within 'se' is 'swee'.
'swee'+'t'='SWEET'
Can you help me to learn more?
(Other definitions for sweet that I've seen before include "Pleasing" , "Humbug!" , "Afters" , "Sour companion" , "Sugary - but might be tart!" .)