Why did Jim sneak away from the stockade rather than tell his friends he was leaving?

After a private meeting with Livesey, Trelawney and Smollett, the doctor leaves the compound, with pistols, a cutlass and the treasure map. Jim guesses that he has gone to see Ben Gunn. Bored and scared of the blood and bodies, Jim decides to leave the compound to look for Gunn's boat, although the knows that it is against the wishes of his comrades.