Marriage following conclusion of dogged flirtation (9)
I believe the answer is:
dalliance
'flirtation' is the definition.
(both can mean a casual relationship)
'marriage following conclusion of dogged' is the wordplay.
'marriage' becomes 'alliance' (I've seen this before).
'following' says to put letters next to each other.
'conclusion of' suggests the final letters.
The final letter of 'dogged' is 'd'.
'alliance' after 'd' is 'DALLIANCE'.
(Other definitions for dalliance that I've seen before include "time-wasting action" , "Playing" , "Casual friendship" , "A casual romance" , "Fling" .)