Gangster and sweetheart getting everywhere (3,4)
I believe the answer is:
all over
'everywhere' is the definition.
(I've seen this before)
'gangster and sweetheart' is the wordplay.
'gangster' becomes 'al' (Al Capone).
'and' means one lot of letters go next to another.
'sweetheart' becomes 'lover' (I've seen this before).
'al'+'lover'='ALL-OVER'
'getting' is the link.
(Other definitions for all over that I've seen before include "Everywhere (bar the shouting?)" , "Obsessed with" , "Finished" , "very characteristically" , "covering everything" .)