Thought a lot about smut-free retrospective (5,2)
I believe the answer is:
dwelt on
'thought' is the definition.
Although both the answer and definition are past participle verbs, I cannot see how they can define each other.
'a lot about smut-free retrospective' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'lot' is 'lto' which is within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for dwelt on that I've seen before include "Brooded about" , "Lingered over" .)