Ace lied when he said he hadn't seen his little brother in three years. Ego and something else he guessed must be a fierce protectiveness that had germinated over the years of living with an idiot like Luffy prevented him from admitting the truth about his trips away from the crew. He was never gone long enough for curiosity, racing back on his skiff after affirming Luffy had not gotten himself killed or maimed or anything of the sort just yet. The boy and his crew had no hint of their transient guardian, but for Ace it was enough to relieve his anxiety for a little longer.