Drama Drama Drama

[Queen of the Ryche]

So here it is. Long story that I really need to get off my chest. One of my so-called best friends comes to me a year ago and says this guy has been flirting with her, and it makes her feel really good, because she feels kinda taken for granted by her husband, who also happens to be one of my closest friends. A little time goes by, and she tells me don't tell anyone, but she's been fooling around with this guy. More time goes by, I don't hear any more, i kind of forget about it and assume it's over.
Flash forward to last week - the "friend's" sister in law comes to me and says she just found out that this "friend" has been cheating on her husband, everyone in the family knows, don't tell the husband, because she's confronting the "friend" and letting her know if she doesn't come clean with her husband, then she, the sis in law is going to tell him.
The "friend" tries to lie, says it was only flirting, nothing happened - eventually comes clean.
Now here's the good part; the hubby/my friend is pissed that we (the sis in law, me, etc) didn't tell him as soon as we found out. We tried to explain we wanted his own wife to tell him. It was her mess, she needed to clean it up. Also I come to find out that she told him that I knew all along, and I was okay with it, and now I'm a back stabber for not being okay with it now that everyone else knows.
How do I get over the fact that I didn't ask to be brought into this, and I don't want to the husband to think I kept it from him because I was okay with it, I was just trying to keep a promise to my so called "friend."
I'm sick to my stomach over this. I already lost one so-called friend, I don't want to lose the other.