"Loner" is a single line, but it holds a surprising idea. The speaker says that the more time they spend alone, the less lonely they feel. That runs against what most of us expect. We usually treat being alone and being lonely as the same thing, and the poem quietly pulls them apart.
The speaker sounds calm, even settled. There's no complaint here and no pleading for company. Instead, solitude seems to have become familiar, maybe even comforting. The word "stay" suggests a choice, as if the speaker keeps returning to being alone rather than being stuck there. Loneliness, the line implies, may come from longing for other people, and that longing fades once you stop fighting your own company.
The mood is quiet and reflective, with a hint of wry honesty. The title, "Loner," could sound like a label others put on the speaker, but the line reclaims it. It leaves us wondering whether this peace is real contentment or something the speaker has gotten used to.