I don't really have any advice either. Even if you son doesn't have any mutations identified yet, he still has some health issues. His health has improved with treatments. Even though he's your son's father, would it be possible to NOT share so much information with him in terms of appointments being that he's being a detriment to your son's health?
When DS was diagnosed at birth there was some confusion --- normal sweat tests, a couple of inconclusive blood tests and one positive blood test --- so DH and I were in a little bit of denial. However, we continued to do his treatments and figured that "down the line when someone would tell us it was all a mistake, that DS would have the healthiest lungs around". <img src="i/expressions/face-icon-small-smile.gif" border="0"> Unfortunately, he DOES have CF and when he cultured Pseudomonas at 3 months old it pretty much brought us to that reality.
Hopefully some other parents will have some suggestions. I seem to recall a parent with a similar issue here a year or so ago -- the dad would go so far as to run the vest without the child in it, just so it appeared they were doing treatments. <img src="i/expressions/face-icon-small-sad.gif" border="0">