Have you tried different foods? My girl, Chappy, doesn't like flake or pellet food, but she loves worms and krill! I had the same problem when I first got her.
well I guess all you can do is watch him and if he starts looking sick do something then, but like we've said keep trying to feed him and hopefully he'll eat soon.
Hmm I had this issue with my two females when I first got them. They wouldn't eat for a few weeks. I switched to Hikari Betta BioGold, and they really seem to like those. Now they can't wait to eat! They hated the other food I got for them initially. I've tried feeding them the old food on occasion and they still refused them.. so maybe try buying a few foods and seeing if any of them seem to please your little fish more. :)
My new Betta doesn't want to eat either. A lot of things I've read say that they need time to adjust from the transition of store to tank. Hang in there <3 I hope he starts eating soon. He really is very pretty.