The sporadic use of Bi-PAP for obstructive sleep apnea (OSA) may confer some benefit but, at best, much less than consistent use of Bi-PAP. A person who uses this mode of treatment in a sporadic way is not really treating his OSA.
And, there is a relationship between OSA and diabetes to the extent that the treatment of OSA often reduces the severity and increases the ease of control of diabetes. Most important is that smoking and being extremely overweight makes both conditions worse. Regardless of whatever other treatment this man takes, he will remain in poor health if he does not lose weight, control his OSA with the Bi-PAP and treat his diabetes optimally.