Millay's poem is a tongue in cheek demonstration of the principle of revealed preference: What individuals want is demonstrated by what they do. She insults the god of love in terms designed to imply that she does not want what he is handing out ("Who still am free, unto no querulous care/A fool").
The predictable result of
insulting the god of love is that he will shoot her. Being
shot by him means falling in love. So the fact that she
insults him implies that she wants to be in love–as she
concedes in the final couplet.