The speaker is addressing someone who has no idea how they feel. Everything hangs on the word "oblivious," which comes back again and again, like a small complaint the speaker can't stop making. The person doesn't see that the speaker is waiting around, doesn't see that they still care, and doesn't see that they never stopped being there.
What makes the poem hurt is how quiet it is. There's no anger or dramatic confession, just short lines and a lot of white space, which feels like the pause of someone holding back. The shift near the end is the most telling part. "Have always / And will never / Stop" sounds like a promise, but it also sounds like a trap, since the speaker admits they can't walk away even if they want to.
The mood is wistful and a little resigned. It's the feeling of loving someone in silence, half hoping they'll finally notice and half knowing they won't.