Back with first of girlfriends, very excited (4)
I believe the answer is:
agog
'very excited' is the definition.
(I've seen this before)
'back with first of girlfriends' is the wordplay.
'back' becomes 'ago' ('ago' can be a synonym of 'back'**).
'with' means one lot of letters go next to another.
'first of' indicates taking the first letters.
The first letter of 'girlfriends' is 'g'.
'ago'+'g'='AGOG'
(Other definitions for agog that I've seen before include "Very eager (to see or hear something)" , "Expectant, eager" , "Eager or curious" , "Bug-eyed" , "Excitedly eager" .)