N1
だに
Just, Even just, Even merely
彼のことを思い出すだに、悲しくなります。
Just remembering about him makes me sad.
Explanation
「Vだに」 means 'just by ...ing, already ...'. You do not have to live through it; merely thinking of it or hearing of it brings fear, grief or a shudder.
Examples: 「想像するだに恐ろしい事故だ」 (It is an accident that is frightening just to imagine), 「あの悲惨な光景は、思い出すだに胸が張り裂けそうだ」 (Just remembering that terrible scene nearly breaks my heart).
It is mostly used with verbs of thinking, hearing or seeing: 想像する, 考える, 思う, 思い出す, 聞く, 見る.
The ending is usually a strong negative feeling such as 「恐ろしい」, 「身の毛がよだつ」, 「胸が痛む」 or 「ゾッとする」.
Mixed up with
「〜だけで」: everyday; works with any action verb, as in 「見るだけでわかる」.
「〜だに」: elegant written style, mostly with verbs of thinking, hearing or seeing, and the ending is usually a strong negative feeling.
「noun＋だに＋しない」 is a different pattern (see 「だに + しない」): with a negative it means 'not even', as in 「微動だにしない」 (not move even slightly), 「夢にだに思わなかった」 (never even dreamed of it).