He's probably just very excited of getting his business going, and still loves you just as much.
It's the old "taking those around me for granted" syndrome. You've been together for 3 years, he probably feels secure and safe and thinks "yeahhhh I don't need to try as hard anymore" which is complete caca :p. He can not take you for granted, ask him soon if there is maybe just some time you guys could spend alone together.
I doubt he'll cheat on you, I can't give you reasons why, other than if he's still with you and starting a business, he's keeping you in his plans.
How long has this business thing been going on for?
