Sleeping after work could indicate exhaustion. It sounds like he works long hours, at 12 hours a day. Is he completing tasks of daily living, such as good hygiene, eating well and accomplishing other daily tasks? If not, then he may be suffering from depression, which could be exaccerbated by his current emotional family situation. It would benefit him to have a physical exam done, along with blood tests, to be sure that everything is within normal limits. He should also speak with the doctor or a therapist about current issues that may be troubling him. At his age of 28 it may be difficult for you to intervene even though you want to help him. Be there for him, as you have been, regardless of his father's presence. Make recommendations for help so he can feel better, but remember that he will have to make the decision to help himself, since this is not life threatening at this time. If he becomes despondent and unable to work, then you will need to step in and get him help.
I hope all will be well with your son and you!