Every time Rupert did something that made Nate uncomfortable, he could explain it away or ignore it. Rupert made him feel special. The way he longed to be special to his father and Ted. But when Rupert acted in a way that was morally reprehensible to Nate AND invited Nate to join him in something that could cause not only serious pain to himself but also to the woman he loved, he knew there was no explanation or justification. He could no longer be blind to Rupert’s true self. Nates problem was always his ego, never his ability to read people or his grasp on the difference between right and wrong. The sort of world Rupert was really offering him was one bereft of true friendship, human connection, love. Things Nate actually yearns for and he’s already thrown his friends away for Rupert, he’s not going to throw Jade away too. So he’s got to get out of there before it’s too late.
I think we are too understand that they are a family even if they are no longer married or in love. The happy ending was Henry’s happy ending. His family is united and healthy