And now, as the night was senescent (line 30)
The speaker doesn't know where he is or what month or day it is, but he's really plugged into the natural world. He's watching the stars, and he can feel the night fading. In a way, this poem seems to move to the rhythms of nature and the world much more than to clock time. If this guy wasn't so crazy with sadness, he'd be at home in bed, instead of out wandering in the lonesome forest.
Then my heart it grew ashen and sober As the leaves that were crispèd and sere— (lines 82-3)
This is one of a bunch of moments where the poem uses a simile to tie the natural world to the speaker's feelings. It's like the trees and his heart are vibrating at the same frequency. Suddenly, in this moment, they are joined, and the death and sadness outside becomes the same as what's happening inside the speaker.