After gallivanting, in with flush, high card too much to expect? (7,8)
I believe the answer is:
wishful thinking
'too much to expect?' is the definition.
'after gallivanting in with flush high card' is the wordplay.
'after gallivanting' is an anagram indicator.
'high card' becomes 'king'.
'in'+'with'+'flush'='inwithflush'
'inwithflush' anagrammed gives 'wishfulthin'.
'wishfulthin'+'king'='WISHFUL THINKING'
(Other definitions for wishful thinking that I've seen before include "pure fantasy" , "over-optimistic expectation" .)