If we are going to be translating this excellent poem with poetic license, which I can see very well, I am going to offer my own humble translation, now:

Do not wish anything from anyone,
do not think that one can be grateful.
Everyone is thankless, kindness yields naught
but is only wearisome; it only brings harm.
Thus I perceive,
I, so gravely, so acridly angered and vexed
by no one as much as you,
who thinks, so wrongly, that I'm your only friend.

The last two lines in the Latin are hard to make into poetry - they form the last 4 lines of my poem. the "so wrongly" was put in merely to represent the fact that, as I see it, Catullus obviously does not view himself as a friend of this man - and I needed to find something to make the rhythm more natural.

To elaborate on the idea that Catullus is pissed off at someone, I think that specifically, Catullus i upset at someone who has fallen in love with him, or something to that extent. He is lamenting about how someone could just fall in love with him like that, when Lesbia is too far away for him to grasp, she whom he tries so hard to catch.
After realizing that his kindness and love toward Lesbia has brought him back approximatly nil, he truley realizes the futility of his actions when Mr. or Mrs. Jo or Joanna Schmo falls in love with him. He, therefore, writes about how futile his attempts at Lesbia are (and ergo how much all kindess is), the understanding of which is sparked by the love of the mystery, which is why he hates the mystery so much: he wants to be dissilusioned.
That is my two pence.