Here the man is mad at his friend but his friend doesn't care so he's laughing at him. Here is where his friend turns into his foe.
Third stanza
In the night the man shows his true feelings because he can't end the friendship because it's toxic.
Fourth stanza
Here the man was fed up with his friend not caring about how he was treating him so he plants poison into the apples since he knows his friend likes apples.
Here the friendship finally ended, the man was set free from the toxicity.