It doesn't sound like Sun is a person you can trust to be ethical in a divorce. He can't be ethical to you, his other partner, not even his children in everyday life. How do you think he will be when it comes to legally ending this mess and settling custody of the kids?
If any of what he says about his new partner is true, do you want her influencing your kids? Do you want to deal with establishing a new set of standards in your home only to have it made twice as hard because he has some warped way of parenting where they feel forced to sleep in his bed and overly aware that he is rubbing one out to porn right there near the bed he insists they sleep in?
I've read that you intend this relationship to end and I see nothing that should make that intention a bad one; quite the opposite. As a mother, I'd be compiling evidence to use because 1. he has threatened to do so himself 2. he already sounds mentally abusive to you AND the kids now and who knows what level that will ramp up to without you around. 3. He works away from home right? How is a shared custody situation going to work if he settles near his job? 4. How much do you want your children to be exposed to someone who carries a flask all day and drives drunk?
I really feel for you and your situation. But now is not the time to get overwhelmed with grief. Sure divorce will end the daily misery for you, the daily arguments the kids are witnessing, but the aftermath HAS to be in the kids' best interests and ask yourself honestly, do you think he can manage that during the divorce process?