This fucked me up inside even more TT TT
ouch
Sakura (MC who is alive) did not reject him. He said he should have been the one who confessed first back then, which tells us that he had already made Arimura (ghost) aware that he used to love him too. He admitted that he always left everything to Arimura, which is why this unfortunate situation happened.
When Arimura (ghost) said it was impossible for Sakura to say “I love you” first because he wouldn’t even accept his invitations to drink or go mountain climbing, Sakura replied that while Arimura was still lingering with regrets, he had already changed. Basically: “I used to deny my feelings for you, but I’ve changed as a person. Many years have passed and things have changed. You’re still lingering with regrets, but I've accepted it."
After that, Arimura is no longer in the room, so we can infer that he finally let go of his regrets after knowing that Sakura had also moved on from their mutual regret.
But Sakura is later shown much older and still returning to that room. This means that he only said those things to give Arimura the reassurance he needed to move on, even though he himself had not truly moved on. He still regrets that he “did not take the first step to confess” before Arimura died and says he is still not finished “clearing his debts from the past.”
So, while Sakura helped Arimura attain peace, he himself is still not at peace and continues to carry his own regret. He said himself that “it’s going to take a little more time” to clear his debts, probably for the rest of his life until he dies and get reunited with Arimura.
I can't find much information about this manga, but chatgpt (yes, take this with a grain of salt) says that Hidaka Shoko, the author, apparently included an afterword joking about how Arimura (the ghost) never really passes on and might still be lingering around Sakura (the MC).
So it’s about regretting not confessing to someone you love.due to that regret(and the lingering attachments he has for sakurai) the black hair guy arrives in the reference room at particular hour even after his death and confessed his feelings.the white hair guy says he is changed and that he no longer had feelings towards the black hair guy which helps the black hair to finally let go of his attachments as sakurai rejected him(something like that).since then the black hair dude doesn’t come anymore as he has finally Rest In Peace.meanwhile, the white hair dude again regrets his actions and hoping the black hair dude would appear again he goes to the reference room during that particular hour.he deems his action (where he couldn’t confess his feelings toward the black hair guy) as a debt and oneday when his debt is cleared he will be able to meet the black hair guy again.
P.s : it’s based on my understanding T_T