Update: according to a recent Daily Mail article ( 12 March 2016) that I read today, Thomas van Straubenzee and Lady Melissa Percy are indeed divorced [decree nisi?] as of March 2016 on the grounds of his "unreasonable behaviour".
Unfortunately, the article is not particularly accurate, calling Van Straubenzee the best man at the Royal Wedding. The article implied a relationship between van Straubenzee and Sophie Carter, two of the godparents of Princess Charlotte, who went with the Cambridges on their Courchevel skiing holiday. It however admitted that Sophie Carter, a friend of the Duchess, has a boyfriend, so I doubt that the claimed relationship exists
Source:
Ben Ellery. "Did Kate and Wills have their work cut out as matchmakers for newly divorced Thomas van Straubenzee and his old flame?" Daily Mail, 12 March 2016
http://www.dailymail.co.uk/news/article-3489644/Did-Kate-Wills-work-cut-matchmakers-newly-divorced-Thomas-van-Straubenzee-old-flame.html"The three-year marriage of Old Harrovian van Straubenzee and Lady Melissa Percy, 28, ended in a ‘quickie divorce’ earlier this month.In a hearing that lasted barely 45 seconds at the Central Family Court in London, Lady Melissa, 28 – the daughter of the Duke of Northumberland –was granted a decree nisi on the grounds of ‘unreasonable behaviour’ by her husband.
The article said earlier that the divorce wouldn't be finalized for six more weeks, so technically they are still married (decree absolute not yet) and could still reconcile as the Earl of Calendon and his second wife Henrietta did, briefly.
No comments on the breakdown of both Percy daughters' marriages, but both weddings were attended by the younger British royals.