Loneliness is the whole subject here, though the speaker never uses the word. They simply describe a habit: piling many pillows onto the bed each night so they won't feel alone. The admission is plain and a little shy, and that plainness is what makes it land.
The pillows are doing a job a person might do. They fill the empty space, offer something to hold or lean against, and create the feeling of someone nearby. The speaker seems to know this is a small, makeshift fix, since they say it happens "every night." That repetition suggests the loneliness is not a passing mood but something they return to again and again.
The title, "Every Night I," cuts off before it finishes, which gives the poem an unfinished, trailing feeling, as if the thought is too tender to complete. The mood is quiet, vulnerable, and gently sad, with a touch of resourcefulness in how the speaker copes.