Maybe Simon stayed the duration of the planned trip? I mean, why leave a trip early to go back to a wife you're fighting with and an uncomfortable home life?
If she flew back to Perth alone, as he said she did, then Simon had a 4 month old child with him. I'm thinking he may have returned to the relatives that they visited up there in QLD for assistance with that.
Who knows? I guess if the question isn't asked then the witness doesn't provide all of the details.