How pointless to follow a girl in a state (5)
I believe the answer is:
idaho
'in a state' is the definition.
(I've seen this before)
'how pointless to follow a girl' is the wordplay.
'how pointless' becomes 'ho' (I can't justify this - if you can you should give a lot more credence to this answer).
'to follow' means one lot of letters go next to another (some letters go after or follow others).
'a girl' becomes 'Ida'.
'ho' after 'ida' is 'IDAHO'.
Can you help me to learn more?
(Other definitions for idaho that I've seen before include "State of north-west USA" , "One of 22 Across, capital Boise" , "somewhere in the US" , "American state, capital Boise (5)" , "My Own Private -- (1991 film)" .)