I only dared to say something so intense because it was to you.
This is the adverb version of the kanji daring, so it means dare to or daringly.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You haven't learned this reading yet so here's a mnemonic to help you:
You're about to daringly jump off a cliff and you shout, "AAAHHH (あ)!" to get your courage up! You always have to yell AAHH before you dare to do daring things!