Hi, I can help you today.
His marriage may be "beyond repair" but what he wants, an "amicable" divorce is not reality. He is "cheating" and she is not happy with him and probably stays for the lifestyle. Going to take a lot for him to leave and it will probably never happen. If he wanted to get a divorce he would get it, amicable or not. Do you think that there is a future for the two of you or do you question his reasoning for not getting divorced? If she won't go for it then they are both willing to be miserable together. There is always a chance but I wouldn't invest much time in this relationship if you are looking for permanence.
Please accept and feel free to comment on this response.