Someone as far gone as the man had to be to fly his plane into a building just might be a little hard to live with.
I can imagine a situation where she would leave the home because he was insufferable, and a motel is a likely sanctuary.
Of course, such a domestic dispute (I have no evidence either way--might not have happened) could lead him to reach the mental state where he was irrational and decided to burn down the house, etc.
Whatever the situation, he might have been better to join a church than try to scam by as one.
He had been planning this for months. Quite coincidental that she happened to 'check out' the night before.