That is my advice.
Why would I give her advice on how to make her friends boyfriend either cheat on her, or break up with her.
If it's advice you want me to add then it would be to go out and meet some new people, either romantically or just friends. Or take up an activity to help you forget about the situation.
I'm sorry if I misunderstood the question, I thought she was asking what to do about the situation, I told her to forget about the guy as he is taken.