I am glad that you are standing by your values and I hope that you do work things out with your husband. Every relationship has had its fair share of hardship - but cooperative perseverance and effort can help overcome even the hardest times.
I would expect that a friend would advise and encourage you to work things out...rather than to suggest you to cheat and to lie to your husband.
Now I'm not implying that you should end your friendship...however, the "advice" she has given speaks volumes about her character and her beliefs.
In today's instant-gratification obsessed society, for some, they may find it easier to cheat rather than to confront their partner and work towards a solution. Sex and companionship can be easily found through the Internet, and there are even websites catered to unhappy, married persons.
I know of many women that have cheated, and frankly, they act as if it is the norm. These are the everyday, average working women mind you...co-workers, acquaintances, neighbours etc. I believe that at one time in their lives, they came to a point where you are at now.
But the difference between you, them, and your friend is that you are a fighter.
Do what you believe is right for your relationship...rather than take advice which goes against your beliefs, and from a friend who maybe cannot understand where you're coming from...