Jack is difficult to hide. The truest disguise, Stephen knows, is one which draws on the truth. Though what truth there was in the bear costume, perhaps it is best not to ponder. As a whaler he's more convincing, yellow hair loose and flying, face alight with the joy of wind and war.
Jack cannot hide as Stephen can, behind command of languages, a particular sense of propriety, an understanding of the turn of life on land. Nor can he hide emotion behind guarded eyes, anger released through the pen, desire, well. That Jack most certainly cannot hide for long.
But when they two can hide together, oh joy! When truths are told and scars are tasted, when Jack's hands are gentle and Stephen's demanding, when sweat and the salt of the sea mingle on slick bodies, then.
Then the disguise of best friends is made convincing by the truth of lovers.