The Cause of Paul's Jealous Paranoia
I thought it was obvious.
The basic factors that can make any marriage deteriorate.
His long hours at work and the son distancing him from emotional and physical intimacy with his wife....
She can't live with that void so she busies herself with the child, shopping, her mother, friends, and guests in the hotel.
The lack of communication and time devoted together and the fracture of trust caused by this lacking allows the paranoia to develop.