As general rule in immigration law, as long as two people enter into a good faith marriage with the intention of establishing a life together and not for the purpose of getting an immigration benefit, then no fraud is being committed. It is possible that marriages entered into in good faith can end later for different reasons. Your friend should fully discuss his case with an attorney to make sure there aren't any immigration consequences later.
Legal disclaimer: By answering this question, there is no intention to create, nor does it create an ongoing duty to respond to questions. An attorney-client relationship has not been formed. The answer is not intended as anything other than the opinion of the author. It should not be relied upon as legal advice. The answer given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change.
If he is no longer in love with her or believes that his wife will divorce him, then it seems that he may be in his best interests at this point. Filing an application and adjustment carries financial consequences that can be enforced in divorce court.
She may want to move on with another relationship. She may be extremely upset with him when she finds out about his infidelity. He really needs to use care at this point. Although the relationship may have been entered in good faith, it is unclear if the marriage is viable, which can create complications for him and his wife.
In addition, she may have options and the decision to continue with a visa petition may prove unwise for both of them.
This is general information, not legal advice, and does not create an attorney client relationship.
There may be bad judgment on his part, but I don't see any immigration fraud.
(213) 394-4554 x0 Mr. Shusterman is a former INS Trial Attorney (1976-82) with over 35 years of immigration experience. His response to your question is general in nature, as not all the facts are known to him. You should retain an attorney experienced in immigration law to review all the facts in your case in order to receive advice specific to your case. Mr. Shusterman's statement above does not create an attorney/client relationship.