I think I suffer from envy? How do I overcome it?

I couldn't figure out for sometime why I felt a bit bitter towards one of my friends. Then I read Bertrand Russell's book Conquest of Happiness and it says that 'virtuous women often envy non-virtuous women who go unpunished' etc etc. and I thought maybe that's what is happening. My friend has a boyfriend who is crazy about her and she is seeing him secretly and behaving really wildly with him. I don't have a bf, and maybe I feel envious of her. How do I overcome these feelings? I dont want to hate her because of what she is doing, as it really is none of my business. but i can't seem to feel the same degree of friendliness towards her as i did before?