One collecting things up, philanderer beginning to repent (5)
I believe the answer is:
raker
'one collecting things up' is the definition.
'philanderer beginning to repent' is the wordplay.
'philanderer' becomes 'rake'.
'beginning to' says to take the initial letters.
The first letter of 'repent' is 'r'.
'rake'+'r'='RAKER'
(Other definitions for raker that I've seen before include "One levelling the ground" , "a sail to the moon?" , "One clearing up leaves" , "One gathering up leaves perhaps" .)