That’s a very interesting angle. Hadn’t considered a breakup due to her blowing away his $$. Then, she up and runs away to another country out of fear. In his unbalanced state, he reserves the room at the hotel in her name (unconsious wish to get her back?).
As good a bit of speculation as any!
When I first heard that she was out of the country I had decided that she was was a muslim who had brainwashed him and left Dodge before the crime. But as I learned of him being an unfriendly loner, aggressively standoffish to any neighbours, but with some money and a girlfriend, I changed my thinking. I think she had made good use of him and was done. She also had to know he had weapons and wanted to be far away after jilting him.