This is the correct answer as Othello states, "If that thou be'st a devil, I cannot kill thee," which allows the reader to infer that even if he/she/they are the evilest being on all of Earth, Othello will not be able to kill them due to her sadness. Thus, this excerpt expresses her true weakness that is sadness.
<em>"I'd have thee live; For in my sense, 'tis happiness to die"</em>
Othello is so sad that killing Iago would be a free pass. Othello's desire is to have Iago living with all the disgrace, guilt, and shame that he managed to collect so someone will feel as disgraced as Othello does, perhaps. Specially the one responsible for all.
