Answer:
D). It is hard to leave your friends behind, and it is challenging to forget the mistakes you have made.
Step-by-step explanation:
The key idea that the author wishes to convey through the given poem is that 'leaving the friends behind is difficult and it is even stretching to ignore the mistakes or follies that we've committed in our life.' This challenging state of mind is clearly reflected through the descriptions like 'darkened mood, dismissed feeling, disappointed look, etc.' Thus, the speaker feels regretful and dispirited and hence, option D is the correct answer.