Dated plot for 2012
The premise might have made sense in the original 1995 book, however, 17 years on I find it unlikely, particularly given the family is clearly affluent, educated, and worldly. The marriage was already on the rocks so it's unlikely in 2010 that an announcement that he's gay would be much cause for amazement.
This reminds me of "Deep End" (a great Tila Swindon performance) filmed in 2001 and based on the 1940s book "The Blank Wall". The original premise, that a mother protects her daughter from the scandel of her getting involved with an older man, would be laughable in the present century. So it was updated to a teenage son involved with an older man. But then again eleven yers on in 2012 even that doesn't make sense any more, particularly in a clearly affluent and evidently non-religious Lake Tahoe family.