Yet this inconstancy is such, As you too shall adore;
At the beginning of the third stanza, the speaker's all, "but it's cool, Lucasta, because you'll like the fact that I'm sort of stepping out on you with, you know, war."
That's what he means when he says she'll "adore" his "inconstancy" or unfaithfulness. Apparently, it's "such as" or the kind of unfaithfulness that she'll be on board with.
I could not love thee, Dear, so much, Loved I not honour more.
Ah, so now we get every part of the poem tied up in a neat little bow.
Apparently, Lucasta will totally adore the speaker's inconstancy because he couldn't love her as much as he does if he didn't love honor even more.
And that mysterious remark answers the question of what it is about warfare that has our speaker so passionate: honor.
If we understand that correctly, we take it to mean that his greater love of honor is what ultimately makes him capable of loving a woman. Hmmm. That's new.
We can't help but wonder if this grand finale is really going to placate this Lucasta lady. But we guess that's a question only she can answer.
Finally, did you notice that this poem has a rhyme scheme and a definite structure to it? That's because it's written in ballad meter, and for more on that, you'll just have to check out our "Form and Meter" section.