After i've arrested young Livingsten and trigger Lind event i noticed another traitor in my castle. However after 35 hours play the game i'm still can't find clue about the traitor.

Also there is something in my mind that i made mistake. I should finish Lind event before arresting young Livingsten.

If that's the true storyline, the traitor problem finished after Livingsten event.

Can anyone tell me how to find the clue about the traitor? Or i've made wrong storyline?

Those two quest are unrelated, and the order in which you do them is irrelevant.
Yes, there is more than one greedy noble in your castle, who want you dead. :D But many story lines in the game aren't done yet.