Romeo is expressing the feelings he has towards the idea of “love” and how horrible it can become.
Friar Lawrence is explaining how Juliet needs to be careful wile all of the craziness around her continues to escalate.
Poison, both sleep inducing and lethal, is the instrument of Romeo and Juliet's deaths. (Technically Juliet stabbed herself, but that never would have happened if not for the sleeping potion.) While poison has a literal purpose in the play, it's also a symbol. The poison symbolizes the Capulet and Montague feud. Not only is the feud deadly in itself, — recall Mercutio's death — it's also the catalyst for Romeo and Juliet's double suicide.
Clearly,