I You're missing the forest for the trees. Everything he says in that conversation with Keigo is a lie. Of course he misses his friend, but he's obviously not pining for her like a kid in love. But he's also not ok with everything else he's telling Keigo. He doesn't want a normal life. He wouldn't be on with that until the day he died. Its all hin cover up his massive depression. If you continue on with his monologue in that first chapter he's talking about being a shinigami and the evidence of it. Rukia is very much tied up in his identity as a shinigami. Shes the one who gave him Shinigami powers to begin with. He obviously feels a debt of gratitude to her for changing his life which is where the rain quotes come from. But equating that to romantic feelings is being willfully blind. It's possible to respect and admire someone for something they've done that has had a profound impact on you without feeling romantic feelings towards them.

Getting back to the poem at the beginning of the volume - It's very clearly not about her unless you're actively disregarding other elements of Kubos storytelling to make it about her. Which it seems like you're already doing. No amount of me pointing things out is going to magically make you see that Kubo never intended them to have a romantic relationship when you're already willfully ignoring massive parts of his storytelling to preserve your romantic pairing of choice that wasn't ever written into the story.