The speaker misses someone, and the poem is about how hard that feeling is to explain. It starts with a familiar romantic image, the sun missing the moon, but throws it out almost at once. The speaker points out that the sun and moon never really meet, so the comparison doesn't hold up. It's a neat, slightly cheeky way of saying that the usual poetic language isn't good enough here.
The speaker then reaches for something "more deeply," but the last line doesn't give a bigger image. Instead it circles back: "i miss him like how i miss him." That repetition feels like giving up on metaphor, and also like honesty. The feeling is so specific to this one person that nothing else can stand in for it.
The mood is quiet, plain, and a little raw. The casual lowercase style and missing apostrophes make it sound like a private thought typed out in the middle of the night, which makes the longing feel real and unpolished.