There is a way

If they don't like each other, I think he should stop getting greencard for her, otherwise later on, he will feel used by other poeple.

It is simple, mail the divorce judgement, if the divorce judgement takes some time, then ask the lawyer to write a letter stating that divorce is in the way, mail it to the BCIS. He can also call the immigration lawyer to check if there is a form to fill out.

If the wfie 外遇, she is cheating and she should get what she deverses.