If the BTC's are still there, move them asap to a much secure wallet and probably you will be the only one who knows. Crypto is money and the personal interest of other people with other's fund is there.

I don't know on how long you've been together but with the explanation you have that made me think that your friend(business partner) took it. You don't trust your wallet with any person even it's your friend, I would only trust a bit my wallet to my wife or kids and parents.