Jacques, it sounds like wallflower already knows all that. The issue is the emotional impact it had (which is in the past), not that wallflower still resents the neighbor.
And that money is weird, on an emotional level. Which it is.
> "let me explain the complete context of why $10 was not a generous donation:"
and
> "I thought I had a good relationship with him".
Which I took to mean he still sees it very much that way today.
The whole idea that somehow your friendship status should translate into an obligation to write a check for a minimum of 'x' for a charity that you pick is very strange to me.
As if you can put a price on friendship that way, and as if the 'interesting conversations about life' suddenly were not good or worthless by the act of giving an amount that was deemed too low.
And that money is weird, on an emotional level. Which it is.
(Not that anything you said here is wrong.)