I agree. Stay out of it.just stay out of other people's relationships. period. nobody is going to thank you for breaking them up. If the girl is running around happy as a lark and telling everyone how great it is to be in love then let her be happy.
Also be aware of the true root of the problem -- Fred's drug addiction. Any time there's an addiction in a relationship, it's highly likely that things will not end well.
If the gf learns this lesson, then something good will have come from it.