My mistress' eyes

To me, this poem was really opposite of something one would write to try to tell a girl you love her and she means everything to you. The tone at the beginning of the poem is almost cynical. It is almost as if the speaker has nothing positive to say about his love. I mean it seems as if everything compares to her and is better. A A real love poem would be quite the opposite. For example, her "eyes are nothing like the sun" would be "the sun is nothing compared to her eyes". However, the last two lines of the poem create a shift in tone with the words "and yet". According to the book, the last line can be paraphrased as "as any woman who has been lied to with false comparisons..." The line before that says his love is rare. So putting these two ideas together, I think the speaker is trying to say that when men say things like "the sun is nothing compared to her eyes", it's a lie. Yet, since he is not lying to his love, his love is true? That almost seems paradoxical.