Final answer:
The quote "[He kisses her.] So sweet was ne'er so fatal" is from Shakespeare's play Othello, where it is said by Othello before he kills Desdemona.
Step-by-step explanation:
The line "[He kisses her.] So sweet was ne'er so fatal" is spoken in the Shakespearean play Othello. This line is delivered by Othello himself in Act V, Scene II, when he kisses Desdemona one last time before he murders her, mistakenly believing she has been unfaithful. The tragedy of Othello centers around the noble general who is manipulated by his ensign Iago, leading to jealousy and ultimately the death of both Othello and his wife Desdemona.