| Quote #1
This lime-tree bower my prison! (2)
You could read the beginning in at least two ways. Either the speaker views nature itself as a prison because he has a distorted perspective at the moment, or he views only that nature which has been controlled and domesticated by humans as confining.
| Quote #2
It's as if he thought nature would swallow up his friends and suck them into a black hole – why else would he worry about not seeing them again? Nor do we think it's a coincidence that he imagines them traveling down into a dark ravine here.
| Quote #3
Ah! slowly sink
In the speaker's first attempt at union with nature, he takes kind of a bossy tone, ordering the flowers to do this and the clouds to do that. Actually, he's using an ancient rhetorical device known as apostrophe, in which the speaker demands that nature do everything it is already doing – only better. You'll find this device in a lot of Romantic lyrics.