Answer: The right answer is the A) His heart and spirit to wither like his body.
Explanation: Just to elaborate a little on the answer, it can be added that, in the first stanza, the speaker, after having seen his "wasting skin," a sign of his aging, says: "Would God it came to pass / My heart had shrunk as thin!" This indicates that he still feels young inside, and capable of loving, and this is causing him pain, since often his love is not returned. Therefore, he wishes his heart and spirit to lose vitality and shrink, like his skin, so that he does not desire anymore and can stop experiencing rejection and heartache.