Standard Disclaimer:All characters belong to Oda. I'm just barrowing them for bit.
He knows when they're 10 and Chaka is that school mate who's awkwardly tripping over feet he hasn't yet grown into and understands the difference between "kinda missing his mom" and "being a crybaby who misses his mommy".
He knows when they're 17, inexpertly groping at each other on the bed their discarded robes make on the sand. He rolls on top of Chaka, feels the man's sword calloused hands run up his thighs, and isn't surprised when his confession of never having done this before is replied to by "Neither have I".
He knows when he's stopped by the King to be told that the man would give him one of the country's greatest treasures in return for his loyal service if he hadn't already picked it out for himself. His eyes follow his king's gaze to what he thinks- for a wild, panic filled instant- is a laughing Princess Vivi, then realizes is the sharp featured man she's conversing with who hasn't quite succeeded in hiding the bite mark on his neck.
He knows when he stretches his wings for the first time and finally understands what Chaka's been trying to make him understand since he ate his devil fruit; sharp senses and animal instincts layering his own frame of reference and the best sense of physical freedom he's ever known. He takes off, not bothering to look down because he knows the other man will follow.
He knows, as he streaks upward with his deadly cargo, that his only regret is that he merely assumed Chaka knew that Pell had had every intention of spending the rest of his life with him.