malisvaart:

Neither Dumbledore nor Grindelwald ever seem to have referred to this
brief boyhood friendship in later life. However, there can be no doubt
that Dumbledore delayed, for some five years of turmoil, fatalities, and
disappearances, his attack upon Grindelwald. Was it a lingering
affection for the man
or fear of exposure as his once best friend that
caused Dumbledore to hesitate? Was it only reluctantly that Dumbledore
set out to capture the man he was once so delighted he had met?