Do I tell or Dont tell?

My B-F is married with 4 kids Her life revolves on her family. I can almost say she is perfect, but she has an addiction to crystal meth, her husband thinks she has been clean for 3 yrs. which is not true She has been a user for about 10 yrs. I feal like she needs to come clean but I’m affraid to loose her frienship I need some advice