So far, we have gotten one new question every five lines. But the last two lines give us two different questions.
This line is strangely vague and general. Also, the syntax (the order of words) is gnarled and complicated with all those verbs: "could...have," "done," "being," and "is."
The speaker is simultaneously thinking about some other reality in which Maud Gonne was not such a firebrand or heartbreaker, even as he recognizes that it could never have been any other way.
He decides that there is no point guessing about what could have been and blaming Maud for the way she was born and raised. That's just how she is!
To make matters more confusing, Yeats even manages to squeeze two question words into one question: the line begins, "Why, what..." We would have liked him to work in "how" and "when," too, but not a bad effort as it stands.