Find a truly neutral third party you both respect. Have them sit down with both of you and talk out all the issues. Their job is to provide you both with some outside perspective.
There's actually a whole category of individuals that do this for a living: business counselors/mentors. This is a lot safer than going with a friend you both know, and they don't cost much.
I have used a professional arbitrator in a legal case. I didn't like the result and the other guy didn't like the result, and that was the best we were going to get, so we went with it.