Wow on a first post!! Food for thought.
Personally, I think by his own words and deeds, I think Brian was more of a loner. Needed a lot of downtime. Posts about autism, meditator, lone wilderness trips, and what he said to LE about needing to get away when they fight. That is why he tried to lock Gabby out of the van. By Gabby's own words, she became more agitated when Brian told her to "calm down". And she said she had a fear of being abandoned. She also was upset that Brian had lost confidence in her to make Vanlife work out for them through social media.
I agree with what some WSers have said that both of them were under tremendous pressure to make Vanlife a career and support themselves. Both had saved money for these trips, and per Gabby's dad this was not their first cross country trip. Brian was the one that helped convert the van into living space, per neighbor's accounts. They both wanted this lifestyle.
The incident at the restaurant over a bill indicates to me that money was beginning to become an issue. Also Brian's lessening support over Inst, etc.
And it seems odd to me where they pulled over the van at Spread Creek. No overly scenic place to take photos. I suspect they kept arguing over Brian's behavior at the restaurant, Brian pulled over and went for a walk to cool off, Gabby followed him they started arguing again, became physical and Gabby got killed.
I do think they loved each other but differences in their personalities and coping abilities lead to a horrible outcome. Vanlife brought out the inability of them to cope under this kind of stress.
This is nothing like the Watt's story. There was no outside girl friend, he did not try to hide her body nor was there a pregnancy that we know of....