It looks like you are already involved so give proof to the girls parents and the guys parents of they turn a blind eye or deny it then help to empower your friends wife so she can move on with her life. Try to introduce her to girls you know who the girl can trust.
Having an affair is a big no no and if you and your friend interacts in place with a lot of people seriously just let it out in the open that they are having an affair. People will talk about them they might get shunned or embarrassed.
If that does not work then the girl need to speak to molvi + solicitor and draw out an islamic and legal separation as her husband is treating her like a door mat. I suggest you tell the wife to treat her cheating husband with indifference and show him you know what she does not need him. Tell her to stop doing any chores for him and to go out with friends, if she isn't working tell her to find a job so she is financially independent. From this she can show her husband that she can have a better life without him. Also tell her not act desperate and clingy.