Final answer:
The poem line suggesting sleep difficulties is "Amnesia had steeped in my mind with a saturated nocturnal sweetness", which implies a restless mind often associated with insomnia.
Step-by-step explanation:
The line that supports the conclusion that the speaker is having difficulty sleeping is "Amnesia had steeped in my mind with a saturated nocturnal sweetness" (Option D). This line implies that the speaker's mind is filled with a kind of forgetfulness or inability to think clearly, often associated with the restlessness of not being able to sleep. Moreover, the adjective saturated suggests a deep immersion into a state, indicative of the speaker's struggle with sleep. The references to nocturnal sweetness suggest a certain allure or seduction by the night, which could mean an inability to escape the wakefulness brought on by the evening.