Was he this way before you got married?
Where does he go or stay when he leaves for 8hrs or overnight?
It's difficult to say how to deal with someone who has been this way since you met. You have to ask yourself why you stayed with someone who acted this way, even from the beginning. You have to figure that the relationship between his mother and his father is a relationship he is either consciously or subconsciously mimicking. The question is, what more can you do with someone who lies in counseling and refuses to compromise? You have to decide at this point if this is the relationship that you want to remain in? How will it affect your son as he gets older and more able to understand what's going on. Your son could turn out like his dad, and as an adult, do the same things to his wife, like his father and grandfather before him. The best indicator of future behavior is past behavior, and if this is the way he's always been, its not likely he will change unless something happened bad enough to compel him to change (death, break up) and even then it might not be enough.
He should not be leaving the house for hours at a time without you knowing exactly where he is. He is a married man and an adult, he should be able to have the strength and self control to handle his problems with his wife, like a man, not like a child running away. Don't call it a 'guy thing' because that gives him permission to continue the behaviors. If you want to be closer to his parents, try calling them sometimes. They would probably be surprised and happy to hear from you.
You have to think about your son. How things are affecting him. He is the most important thing right now, because he is innocent and knows nothing about all of these things.I welcome your thoughts, let me know if you want to talk more