The platonic best friend of the opposite sex who the girlfriend used to date?  Platonic relationships between the sexes are extremely difficult (from my own experience, I'm not even sure they're possible, but who knows) - I certainly would be very uncomfortable if my significant other was ditching me to spend time with his best friend, who happens to be a woman he used to date.  It's not even a matter of jealousy, but whether your relationship can survive that or not.  

Given human nature, my less optimistic side says that's very unlikely.  If I'd been the author of this article, I wouldn't have held out too much hope.