Welcome, and so sorry to hear about your situation. Sounds very difficult.
How about the "wives can be won over without a word from your good conduct?" Maybe he should read this scripture and apply it.
He needs to take stock of what he has-a home with a wife and three sons. He stands to lose a great deal. Perhaps you could write him a letter explaining your stand. Give it to him when he is calm. Tell him you do not want him to end up a lonely person that has driven away his family. Tell him you love him (if you still do, and it sounds like you do) and that you are willing to meet him halfway. This does not mean that you go to the KHall, but that you will not oppose him if he goes. He is free to worship as he chooses, and you should be free to do the same. This does not mean that you cannot share family fun, cooking, vacations, etc.
If his family are all witnesses they are likely pressuring him to come back. They are doubtless telling him his sons will die. This may be very upsetting to him, as you can imagine. I kinda feel for him, too.
Keep us posted!