Do we know the manner of death of the other two women? Because I would think it would be out of character for him to attack and kill two people. Shooting two people - yes, but killing by knife or bludgeoning takes a lot of effort and anger. Not something I would think fits his behavior. And then to kill her? I just don’t see this guy becoming a stone cold killer. (AFAIK, he has no violent criminal acts in his past).
My theory - they fight and split up, he’s steamed and takes the van leaving her behind. Later returns, either can’t find her or finds her dead, and takes off for home.
Not defending the guy, but his actions don’t seem to be deceptive. If he killed her and left, there was a sizable risk her body would be found before he even got to Florida, and he would have been arrested. The few days spent at home could have been ended at any moment by her discovery, and yet he didn’t.
A fugitive hiding from the law. Deceptive.
There is the possibility BL took Gabby's wallet with both the debit cards he used, and her drivers license. This would delay identification of her body, without the massive search efforts thanks to social media. Perhaps BL tossed Gabby's wallet, along with other personal items belonging to Gabby into the swamp near the Laundrie home. That would support the ongiong search efforts occurring in the swamp.