I'm very sorry :(

There's not much worse than retaliation feedback,
unless of corse you get negative/neutral feedback
for no reason at all (which I have seen happen
too).  I've only left 1 negative and 1 neutral,
though many more deserved it, and was lucky enough
not to recieve any in return, though I completely
expected it to happen.

I have seen people explain their feedback in their
'me' pages, this kind of thing happens a whole
lot.  For a system that is supposed to help
buyers/sellers it also causes a lot of problems. 
Usually when I do business with a person with bad
feedback I look and see what the reason was, even
though most of the people who have wronged lie, 
normally you can tell if the feedback is from
retaliation or not.

I wouldn't worry about it so much, you only have
one and more than likely that wont hinder you in
the future.