I wouldn't be surprised if she threatened to kill herself and he just dipped anyways. Reading the aforementioned tweet as well as
this article makes me a bit more sympathetic towards the dude, although he still could've done it. From the sound of things, she was losing it and he might have reached his breaking point with her when the police got involved. The one part that seems suspect is that when the police told them to separate, he got a hotel and she got the van, so how does he end up at home with the van and without her exactly? Another part that looks sus is that the article said that she was concerned he was going to leave her in Moab (which he ended up doing), so perhaps she wasn't as mentally detached from reality as it seems.
In general tho, the idea of two people with a redacted mental illness doing a cross-country trip while skipping their meds is a recipe for disaster and irresponsible AF.