Continuing sunny at heart, with no money invested (8)
I believe the answer is:
unbroken
'continuing' is the definition.
('unbroken' is associated in meaning with 'continuing')
I don't understand how the remainder of the clue works.
(Other definitions for unbroken that I've seen before include "Complete" , "One" , "Continuous" , "Not interrupted" , "not trained for riding" .)