Sometimes, people need to see another side of their friends to see them that way. That's why it can be better to confess, that way you make them aware of you.
And, when you truly love someone, wanting to share it and claim it is an urge difficult to resist
From my experience, honestly one can never be sure of other person's feelings. And the only (mostly) way to know is by asking or telling. And even if someone does know that other person doesn't hold the same feelings, they just want to express what they feel. That may be a lil selfish but that's just how I see it
I will never understand why people confess their feelings when they know that the other person has no interest in them.. It was always (to me anyway) obvious that Ikkoku did not see her romantically and only as someone who was similar to him, so he could act like himself around her. I understand why she fell for him but oh it’s painful to see her get rejected and for him to feel bad because he doesn’t understand her feelings but he knows that he’s hurt her