Sorry to answer a question with a question, but why do you want to strengthen the relationship, rather than going your separate ways?
A business partnership is similar to a marriage or other very intimate relationship. If you can't have open and honest communication, the relationship will suffer.
In my opinion, once you start to hit the point where you need counseling, it's difficult to pick up the pieces of the relationship - more so than in a marriage, even.
With that said, if you have no option other than to work on the relationship, you need to start at the beginning and work on communication skills. Learn how to listen to each other, and talk to each other. Get vulnerable. Understand each other's feelings, motivations and goals in life.
If you can't start there, then "splitting up the work" is nothing but a band-aid on your relationship that will ultimately hurt or kill your business. In a startup, any sort of work-splitting will be temporary. As the company grows and the business matures and/or flounders, you will need to re-evaluated the work split, your individual roles, and the company's goals.
All of that requires rock solid communication and vulnerability.
If the co-founders are serious about making it work, they will commit to improving the relationship together. That may mean attending events like Landmark Forum or Tony Robbins together. It may mean going through group counseling. More likely, someone will leave the team - if not now, then in the future - either by choice or by force.