There are some things the universe doesn't mess around with. Some things that are constants regardless of everything else. Aeryn Sun was destined to be in John Crichton's life in some way, form, or fashion.
His name was Cameron Mitchell. His father, Jack Crichton, died on his last mission on reentry to earth and his mother married Mr. Mitchell when little Cam was 16 months old. Jack had had his heart set on making his first born son a Junior but Leslie Crichton had always been partial to the name Cameron. Different father, different house, different life and yet he still ended up travelling down wormholes.
He always loved speed, loved to fly, he loved his parents and his mother didn't die of cancer this time around. The universe had stolen his father from him and perhaps in a strange fit of whimsy decided to pretend to be fair and let him keep his mom.
His dad lost his legs this time around. Cameron was twelve. He was the same sunny child he always had been, optimistic and helpful. He helped his dad in the hospital, helped him with his physical therapy and his dad helped him get into the navy and into a plane of his own. He was funny and well-liked in his unit, but with no Olivia in his life he didn't make many pop culture references.
When he crashed his plane in the arctic he got the weirdest sense of dejavu as he screamed "Mayday! Mayday!" into his failing mic. The tailspin crushed his chest and he blacked out for a second, behind his lids he saw another ship and he yanked on the controls, deperately trying to avoid a collision. When he woke up he found he was inches from crashing into the ground and passed out for real.
When she walked into his life with Daniel Jackson he was overhwelmed by the feeling he knew her. Her incessant flirting with Jackson irked him for no reason he could think of and so he avoided them both for a while. But then they discovered she and Jackson couldn't be separated, and then she was part of the team, and all of a sudden part of his life, like Carter or Teal'c. He still tried to stay away but found he couldn't avoid her entirely or avoid worrying about her on off-world missions.
When she was taken he realized how much he'd come to depend on her presence to lighten the mood, to remind him that there was a life outside of the underground fortress in Cheyenne Mountain, a life that Carter and Jackson seemed so intent on forgetting about. They've bonded since then, the flyboy and the con artist. She touches him in simple ways that are devoid of the careful seduction she uses on Daniel. A brush of fingers when passing the syrup they both drown their pancakes in, her hands on his shoulders as they carefully pick their way through Merlin's Amazing Invisible Maze. He's quietly content that she trusts him to see her through danger. She's saved his ass on occasion as well, as accurate with a ZPM in this 'verse as the woman he might have known in another was with a pulse pistol, and possibly twice as unpredictable. They'll probably never get close enough that she'll tell him about her mother and father who defied their commanding officers and escaped an army to have the free-spirit that would become Vala. They may never name stars, or children, or grow old together in the here and now, but somehow he knows in some untapped portion of his brain that she is meant to be a part of his life and he is grateful for it.