Mind my own business or not

[Currant Bun]

Hi all. I'd appreciate some thoughts on this situation.

I've discovered that a female friend of mine is having an affair with one of her hubby's mates. She never says a bad thing about her husband so I'm not sure what prompted her to get involved with another bloke.

Anyway, I care a lot for my friend and would hate for things to go wrong for her if her husband found out about the affair so am tempted to say something to her. At the same time though I'm wondering if it's any of my business and if she'll actually appreciate me getting involved. Anyone else been in a similar situation before?

Thanks in advance.