Is your husband seeing a therapist in Korea? If so, would you be able to attend a session with him to get some information from the therapist? Questions like:
- Is your husband stable enough to try to live in America again?
- Did your husband receive appropriate treatment in Australia and America?
- Is your husband committed to getting better?
- Is there anything you can do to help your husband?
- Does the therapist agree your relationship with your husband is toxic?
- Does he think divorce is the best option.
If the answers are not encouraging, I think you have done what you can to save the relationship. Perhaps because your husband was not forthright about his mental illness, you may be able to get an annulment?
Be well.