Assuming you're in the U.S.: If you don't have a written agreement otherwise, then if you were to "fire" your co-founder, he might nonetheless remain a joint owner of the intellectual property. (The result would be basically the same if you previously formed a corporation or LLC but didn't provide for a break-up in the governing documents.)

If that were the case, then (A) you'd likely have a hard time attracting funding in the future, because your co-founder would still have an ownership claim; (B) your co-founder might well be able to start -- or license someone else to start -- a competing business; (C) your co-founder might be entitled to claim a share of the future profits of the business.

So, if you're going to go your separate ways, you might consider offering to buy out your co-founder, either in cash or for some (capped) percentage royalty on future revenues.

Food for thought.