Nina Dobrev hailed Shaun White as the “greatest boyfriend of all time” following his retirement from competitive snowboarding. The 33-year-old actress has taken to Instagram to lavish praise on Shaun, after he ended his career with a fourth-place finish at the Winter Olympics in Beijing. Alongside a series of throwback images, Nina wrote: “I couldn’t be more proud. Of everything you have accomplished over the last 20 years as a competitor and the man you have become. You are one of a kind.” The ‘Vampire Diaries’ star also claimed that the Winter Olympics mark the “beginning” of a new chapter f…