Four short lines, and the whole poem is one moment: the speaker sees someone standing in the rain and is stopped by how beautiful they look. The feeling is a kind of awe, close to being overwhelmed. Saying that time "pauses" is a way of describing how everything else falls away when you can't stop looking at someone.
The last line is the strangest and most interesting. The speaker says it "bugs my eyes when I open my eyes," which is oddly worded on purpose. It could mean the sight is almost too much to take in, like bright light. Or it might suggest the speaker keeps seeing this image even afterward, so that opening their eyes feels like a small disturbance. The poem doesn't say which, and that leaves it open.
The mood is quiet, hushed and a little dazed. The rain adds softness, and the plain, simple language makes the admiration feel honest rather than showy.