"The moon is beautiful, isn't it?"
It is used to confess to someone you like while under the moon. This phrase is a more poetic way of saying 'I love you'. [it's also an indirect way of saying "I love you"] Japanese itself is a very "indirect" language. You don't have to admit things directly because that's impolite or rude. Why I say that is bcz, Kishi place them under the full moon to share their feelings indirectly and also directly. Japanese people prefer indirect ways of expressing their feelings and emotions. A relationship starts when people tell each other their feelings. Expressing your feelings through words has not always been seen as a natural thing. People express their love and affection through their actions. [Although the main ways of expressing love in Japanese culture differ from Western culture]
What does "friend" mean to you??
[Notice how Sasuke averts his eyes from Naruto (as if he's shy or nervous to get a confession from him) while asking 'what does friend mean to him'?]
Romaji: tomodachi... dakarada
Literal: because we're friends
Raw (Sasuke): それはかつて聞いた... お前にとってのそれは・・・ いったい何なんだ?
Romaji: sore wa katsute kīta ... omae nitotte no sore wa ・・・ ittai nanina nda?
Literal: I heard that before... but what the heck does that mean to you?
[As Naruto continues to give the same 'we're friends' response, he becomes visibly angry, clearly displeased with the answer]
Raw: それ説明しろって言われてもオレも正直よく分かんねェーよそんなの…
Romaji: sore setsumei shiro tte iwarete mo ore mo shōjiki yoku wakanne yo sonna no …
Literal: Even if you ask me to explain it.... I honestly don't properly understand... that kind of thing...
Raw: ただお前のそーゆー背負ってゴチャゴチャしてるとこ見てっと・・なんでか・・
Romaji: tada omae no so you seotte gochagocha shiteru toko mite tto... nande ka ...
Literal: It's just that.... When I see you carrying burden on your back... getting all messed up.... for some reason...
Romaji: ...ore ga... Itate nda
Literal: ...I'm.... hurting...
Raw: すっげー痛くてとてもじゃねーけどそのままほっとけねーん だってばよ!
Romaji: sugge itakute... totemo janē kedo sonomama hottokenē n dattebayo !
Literal: It exceedingly painful. But not just as awfully...as it is now...I can't just leave you alone, dattebayo!
The word Naruto using was 痛く(itaku) meaning- exceedingly or extremely pain. It's not just 'Ouch! It hurts!' kind of pain. It means HE IS IN "EXTREME PAIN". The magnitude and intensity of that 'pain' is so overwhelming that it affects your body and mind.
What was the reason for Naruto & Sasuke's pain to be more emotional??
N. B. When Naruto says that he understands the pain of Gaara's loneliness and Gaara says that he feels pain in his heart... the word used for pain in both cases is 「痛い」 (itaku). 「痛く」 (itaku) is a similar word, but with a more intense and deeper meaning.
Because of those words Naruto says to Sasuke, his face feels a mixture of emotions: touched, or surprised. Sasuke's expression here is probably one of the most emotional expressions you have ever seen. This made him confess his feelings for Naruto (And It was hella poetic (༎ຶ⌑༎ຶ)
In Sasuke's monologue his words are very deep and intense (the choice of Kanjis are complicated). It is also way too direct and carries a lot of intimacy.
Romaji: soshite nazeda ka anshin shita nda
Literal: And I don't know why, somehow.... I felt relieved.
Romaji: daga sore wa ... dōjini yowa sada to omotta
Literal: But... at the same time... I thought It was a weakness.
Raw: だから・・お前の苦しむ姿を見る度・・そう・・・オレも---
Romaji: dakara ... omae no kurushimu sugata o miru tabi ... sō... ore mo...
Literal: that's why. . . Every time I see you appearing to be suffering. . . that's right I, too...
Romaji: ore ga itaku natta nda
Literal: I become pained.
Sasuke also using the same word 『痛く』 and both of them were in such intense pain that words couldn't explain how much it was. It really gives- "If you truly love someone you can feel every joy, sadness and pain of the other as if they were your own". Once you get that, it's easy to understand his reaction to Naruto saying he felt his pain. Sasuke reacted that way because he realized his love was reciprocated. That this feeling of 'friendship' that Naruto was going on about was the same thing that Sasuke had been feeling all this time and it was never friendship. It was more than that. And It was love.