As someone who has never been in this situation, some of the replies in this thread are very disappointing. They basically seem to amount to, "eh, go pound sand, quitter." You've put in a ton of work during the hardest period for a startup. That's not worth nothing. In opposition to these other people, I'd say maybe a frank but congenial discussion with your co-founder is in order. Something along the lines of being…
Ultimately he created very little value and therefore is entitled to very little value. The company can just go out of business and start fresh!
Raising money is not value.
2-5% could be appropriate. 10% is completely insane.