I wonder if Kavanagh had subtitled the poem "Ode to a love affair that never happened" if it would be easier for people to understand. That the hint of bitterness in the poem is directed not at the dark-haired enchantress, but at himself for wasting so much time worshipping from afar and yet imagining himself involved in some relationship which never got off the ground? (The archetypal teenage crush experienced in later life by a man who - as I understand it - was unfulfilled in the romantic/sexual aspect of his life.)

Regarding the "Queen of Hearts" line.

I think this line is difficult to dismiss out of hand. It is undoubtedly more clumsy than many in the poem where Kavanagh's language is exquisitely economical.

As I read it he wanted to make a point about his "still making hay" and needed a point of comparison. The "Queen of Hearts still making tarts" is a metaphor for his object of desire idly carrying on as normal (i.e. ignoring (or being unaware of ) his ardour) while he is "still making hay" - industriously (albeit possibly secretly and - tragically - ultimately futilely) pursuing her.

So whilst I would agree that the line jars a little, I find the contrast startling and it's one of the "hinges" of the poem - a dawning of self-awareness and the key that moves him towards the cataclysmic realisation that there is nothing between them.