This passage is from William Shakespeare's Romeo and Juliet, specifically from Act 5, Scene 3. In this poignant moment, Juliet discovers Romeo dead beside her, having taken poison in despair over her supposed death. In her grief and desperation, she kisses him, hoping to join him in death. When she finds that his lips are still warm, she contemplates the possibility of a lingering poison on them.
Ultimately, she resolves to take her own life with Romeo's dagger, expressing a tragic devotion to him. Her line "O happy dagger!" reflects her decision to use the dagger to end her life, underscoring the play's themes of love, loss, and the devastating consequences of family feuds.
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