Apologies for the misunderstanding. My wife and I are happily married.
I was suggesting, if questioned, the OP should state "My wife and I have separated, but not divorced".
I've known a few change the reason from Thai spouse to retirement, mainly due to requiring less documents and no 30-day under consideration period.
Occasionally an IO would inquire if the spouse was aware of the change, but in most cases they just proceeded with the application.