Everyone's having my career but me

An old friend of mine has recently decided to 'go it alone' and start his own consulting business. He's already had a hugely successful career over twenty years culminating in running one of Australia's largest marketing research firms. Now, after a six-month sabbatical, he's going to start all over again.

Once upon a time my heart would've leapt at the news. Another smart, experienced and articulate mate to bounce around ideas, to celebrate the wins and laugh off the losses. Now I'm not so sure. What if he surpasses in two years what I've built over twenty? I'm wary of a mindset that an acting buddy once described to me as:-

Everyone's having my career but me

I think that a big part of healthily working for yourself means avoiding Gore Vidal's curse ("Every time a friend succeeds I die a little inside").

I need to be secure enough in my own achievements to be able to genuinely celebrate his. What manner of friend am I otherwise?