What's he saying?
"Canst thou, O cruel! say I love thee not, / When I against myself with thee partake?"
Are you really capable of saying that I don't love you, when I am obviously consorting with you against my own better judgment?
"Do I not think on thee, when I forgot / Am of my self, all tyrant, for thy sake?"
Can't you see that I neglect my own interests in favor of you?
"Who hateth thee that I do call my friend, / On whom frown'st thou that I do fawn upon,"
I hate everyone who hates you or whom you hate,
"Nay, if thou lour'st on me, do I not spend / Revenge upon myself with present moan?"
And if you look at me threateningly, I immediately take action against myself.
"What merit do I in my self respect, / That is so proud thy service to despise,"
I have no respect for any part of myself that does not love my duty to you,
"When all my best doth worship thy defect, / Commanded by the motion of thine eyes?"
The best part of me praises even your faults, controlled by whatever you do.
"But, love, hate on, for now I know thy mind, / Those that can see thou lov'st, and I am blind."
But continue to hate me, because now I know what your intentions are; you only love those who see you for what you are, while I am blind with love.
Why is he saying it?
Sonnet 149 is part of the so-called "frenzied" series of sonnets to the dark lady, beginning with Sonnet 147 which states, "My love is as a fever longing still," and continuing until Sonnet 150, which is punctuated by the repeated interjection, "O!". Volatile emotions pervade these sonnets; here, they are most evident in the final couplet, which in its break from the sentiment of the rest of the sonnet seems like a desperate surrender. The interjection "O cruel!" in the first line sets the tone for the panicked, pleading sonnet to follow. It is reminiscent of, "O me!" and "O cunning Love!" in Sonnet 148.
The opening of this sonnet, "Canst thou, O cruel! say I love thee not" seems to be in response to something said by the dark lady, along the lines of, "You don't love me." Various other of Shakespeare's sonnets begin in such a way, and it was conventional for them to do so at the time. For example, Sonnet 109 begins, "O never say that I was false of heart," as if the fair lord had just accused the poet of being unfaithful. Sonnet 117 begins, "Accuse me thus: that I have scanted all / Wherein I should your great deserts repay," as if the fair lord has accused the poet of neglecting him.
The idea that "I against myself with thee partake," put forth in line 3, implies that the speaker is undergoing an internal battle, part of him defending the dark lady against the part of him that knows loving her is futile. The word "partake" means to join someone in taking legal or military action against someone else. The idea as well as the legal terminology echoes Sonnet 35, in which the speaker told the fair lord, "Thy adverse party is thy advocate - / And 'gainst myself a lawful plea commence." Sonnet 35 excuses the fair lord's unfaithfulness to the poet, perhaps with this same dark lady.
In lines 9-10, the poet asserts through a rhetorical question that he does not respect any part of himself that look down upon the dark lady. These lines are reminiscent of earlier sonnets to the fair lord. The phrase "What merit," with respect to the speaker himself, hearkens back to Sonnet 72: "O, lest the world should task you to recite / What merit lived in me..." The idea of being in "service" to the object of the sonnet echoes Sonnet 26, which addresses the fair lord: "Lord of my love, to whom in vassalage / Thy merit hath my duty strongly knit;" these lines also use the word "merit," but in reference to the fair lord rather than to the speaker himself.
The final couplet is not clearly connected to the rest of the sonnet: in it, the poet claims to be blind, but throughout the sonnet he has admitted to her faults. The blindness he describes must just be a symptom of his overwhelming dedication, as it is a symbol for love in general, and his inability to stop loving her despite her poor moral behavior. He encourages her to "hate on;" hatred in the woman to whom a sonnet is addressed was conventional. But although she hates the speaker, she loves "those that can see;" this idea can be explained by the speaker's logic that although he is blind to her faults she still refuses him, she must love only those who are not as devoted to her.
