For him, it's a nice change to go to the theatre with Victor (7)
I believe the answer is:
vincent
'for him' is the definition.
'a nice change to go to the theatre with victor' is the wordplay.
'change' indicates anagramming the letters.
'to go to' says to put letters next to each other.
'the theatre' becomes 'nt' (National Theatre).
'with' indicates putting letters inside.
'victor' becomes 'v' (phonetic alphabet: alpha, bravo, charlie etc.).
'nice' is an anagram of '[nice]'.
'[nice]'+'nt'='incent'
'incent' going around 'v' is 'VINCENT'.
'it's' is the link.
(Other definitions for vincent that I've seen before include "- van Gogh, painter" , "man" , "See 21 Across" , "Van Gogh's first name" , "Van Gogh - saint with a Portuguese cape" .)