You weren't ready for the feelings of emptiness down here.
Every ounce of putrid waste that floats by your nose as you prostrate yourself before the sewage flow reminds you of the millions of people living up above.
You void your own waste into the stream of city's filth. This is the only way that you have to interact with other humans now.
After some time you realize that precisely because of this meager communion, the loneliness you're feeling will probably never fade.
So you go for it. You embrace the loneliness. You cleave to it. The constant ache of it is your rock in times of trouble, your reference point in times of confusion. Your compass. Your companion.
Never mind how you eat.