No. It is never boring. We have been in this life style for over 25 years and during that time my wife has had lovers which have been one nighters to lovers whom have been with her for near on 3 plus years. It would be reasonable to say that all the occasions have had something unique and most certainly never been boring. That is from the husbands perspective and by the looks of my wife afterwards you can see her total enjoyment.
With the question you pose with regards to how often? I do not think there has ever been any rules. It can and has been weekly, also been monthly occasions. Like wise there have been passages of time when she has not had a lover.