I agree that asking such personal questions is rude.
That being said, has this guest been living under a rock for the past ten years? If you call up a daytime show marketed to the SAHM set, in the era of reality tv where no privacy is sacred (they put anyone on tv, duh, first clue), then mention your boyfriend of x number of years when it is totally irrelevant, you are asking to be interrogated about it.
It is also possible this is a ploy to get sonny boy to propose now that his sweetie has been 'embarassed in front of the entire country.' Or a plan to track the 'guest's' wedding plans when sonny boy is goaded off the fence.