unstable middle ground

I need to find a middle ground between taking everything over and focusing on my own life (letting John take responsibility for himself). The trouble is, the middle ground doesn't feel stable. As soon as a problem comes up I feel I have to drop everything and take over. Or it feels like the only way to let him take responsibility for something is to not care whether the job gets done or not.

I have an image that the middle ground is a ridge with a slippery slope on either side. So I need a way to chisel out steps, flat places where I can have a more stable middle ground. My first thought of how to do that is to make a list of what is my responsibilities and what is John's. We talked about it some over dinner and he agreed with the principle that whether he does exercise and activities that will help preserve his quality of life is his responsibility. So I started a list as a shared Google document.