I never have understood the partner thing. All you can do is offer to buy him out, or split the business in half if you dont have the funds to buy him out. I would try to keep everything "cool" so you dont destroy your business, if you are friends its quite possible you wont be if you part ways.
Talk to your partner over a cup of coffee or a beer, <just a couple> and see if you can resolve the mess without much information getting out to your customers. Your partner probably wants out anyway.
Get SOLO and stay SOLO.