The speaker's heart is at odds with his head in this poem. His heart says, "That treacherous Maud Gonne! Look what she did to Ireland! Look what she did to you! We should hate her, oh yes we should!" (Confused? Check out "In a Nutshell.") And then his head comes in and says, "Well, wait a minute. Can you really blame her for being herself? Why are you surprised that she has caused all these problems, if you knew she was always like this? Besides, weren't her passion and troubled beauty what attracted you to her in the first place?" Both sides make a fair point.
The speaker has been heartbroken by the woman in the poem for a long time, to the point that she has filled his "days with misery." However, we think he is in large part to blame for his own unhappiness. His love might be a case of "opposites attract." The woman sounds like an unpredictable fire-starter, while he is more conservative and straight-laced. Notice how he assumes that the working-class protesters that Maud inspires are "ignorant"? The speaker is in love with the idea of tradition, order, and nobility, while it seems the woman just wants to overthrow the established order of British colonization using whatever means possible.
As part of his love for tradition, the speaker enjoys seeing his life through the lens of Greek history and mythology. He's like, "This is just like the time old Helen of Troy started the largest war the ancient world had ever seen." This is a person for whom taking the "long view" of a situation might require looking back at events that happened three thousand years ago, instead of just two or three years ago.