Her only mode? So BL did not take a plane back to florida? I guess she could not fly.
They were supposed to meet friends in yellowstone.
Lets play what if.
So what if they get into a huge argument. He realizes that if the cops show up both of them could go to jail, and being the male, only he will be charged. Just look at the comments in the this forum, he was the aggressor even though she hit him. He says he can not do this any more and she breaks up with him.
She declares that she is going on with friends that are coming from yellowstone to meet her. She then tells him to take the van and the card to get it back to florida. Remember she does not like to drive it.
She goes out to camp, waiting for morning to meet friends. And the same person that killed the couple in utah kills her. The friends shows up and she does not show up. Or she lied about the friends coming.
He uses the credit card to get the van home, thinking she is now having a affair with the new friends and is really upset. He ignores the phone calls, he ignores parents because he thinks she is sleeping with another person.
On sept 11 the parents file a missing person, and he realizes that he was the last person to see her alive. That the friends was either a lie or the killer. He does not know who they are because it was gabbie that talk to them online. The police know of this person from the records, which is why brian was not charge with her murder.
Brian realizes the only person he loves is missing and probably dead. He then wanders into a forest and kills himself.
With this what if, all the marks are checked.
Why was she found away from the camp site in a tent, because she was waiting for friends to show up to pick her up.
Why did he return alone with her van and her cards. She wanted the van to be safe, she let him use the cards to get her van back to florida. Remember she did not like to drive it, so it was either leave it in wyoming or have her parents come get it.
Why did he not contact her parents, she was out with friends that he thought she was having an affair with.
Why did she leave him, because he was done with this van life and she found another ride to finish her trip.
Why did he act normal after he got back, because he did not know she was dead.
Why did he run and kill himself, because he knew he screwed. Protestors outside the house day and night. People proclaiming him the monster. He finds that what he thought was true was not. She was missing and possibly dead.
Once again, if he was going to kill himself over her death, he would have done it in Wyoming. If he was going to run, he would have run in wyoming. In no world do you go home knowing that you killed her.
All wild speculation and my theory.