Loneliness here doesn't arrive with a big event. It slips in through something small: a song. The speaker hears it, feels an odd, heavy emotion, and keeps replaying it, as if trying to understand the feeling by staying close to it. But the feeling doesn't fade when the music does.
What stands out is the speaker's confusion. They are crying without knowing why, and they say so twice, which makes the sadness feel raw and unexplained rather than neatly tied to a cause. The image of claws "deep in your heart" suggests the loneliness isn't gentle; it grips and hurts. The short, plain lines mimic someone sitting quietly, worn down, with little left to say.
The mood is tender, tired, and a bit helpless. The last line, set apart on its own, gives the feeling a face: an "unwelcome companion" that won't leave. Ironically, the speaker is alone, yet not alone, because the loneliness is keeping them company.