Both of them sounds beautiful, poetic, a diary-like writing in Korean.

To me, (1) sounds more like talking to a friend, and (2) sounds a little more like a writing.

But again, both sounds nice and personal. An actress might say this in a drama film.

I think both of them is natural. But in General, this kind of talk is usually said by someone else. I mean, I don't know in which context you want to say this but, maybe you want to talk to your friend or you would be told from your friend that

(지금부터 내가 말할) 그에 대해 알게 될 진실은 생각보다 널 더 아프게 할지도 몰라.

(지금부터 내가 말할) 그에 대한 진실을 알게 된다면 생각보다 너에게 더 큰 상처가 될거야.