[lien]

His doing a startup doesn't prevent you from doing it. An idea is just an idea - it's not a real product and it's not even a patent. There's a lot more to a startup than just an idea, and takes a lot of work.

If you're passionate enough about your idea, you'll find ways to win. Besides, no startup can succeed without competition, so in some ways, he's actually helping you to create or grow this market. Also, he cannot support all of his customers by himself so there will be other customers out there where you could serve.