"Daigo, to Mine, was someone for the first time in ages he genuinely respected and cared for; he loved him like he was his best friend and brother." Mine says he 好きになる for Daigo. 好きになる (Suki ni naru) means "Fell in love with". You cannot use 好き (suki) platonically unless it's something like 大好き or 好きなんだ (daisuki or suki nanda, to like something or someone in general. This is wording better used to say you like food or a movie rather than people tho). Suki is a proper, formal adult love confession (for the record 愛してる ai shiteru is the super over the top dramatic way so adults rarely use it. Hell it's rarely used outside fiction).
You can listen to it again here: https://youtu.be/H00fOtMqh9A?t=8763