Stuck in an awkward position

A few months ago, I accidentally stumbled upon some troubling information about a female relative (who, for the record, is married and has kids); she's apparently been trying to elicit an affair with an old flame (said guy is also married, with kids). Apparently, it started this past fall, via Facebook. I've learned that it's slowly progressed, to texting, and then to long talks on the phone while the husband/ kids are away. I don't think they've actually gotten together yet, but some of the stuff I found implies they've been having phone sex.

How do I know all this? Well, I'll be honest. After I originally caught wind of it, I fell into a bad habit of snooping via her e-mail account (though, she's never made it hard for me to get access; in fact, she often uses my computer, and saved her password on it for her to access easier). I know it's wrong for me to have snooped in the first place, but I couldn't help it. The situation just set off such a red flag to me, that I couldn't stop thinking about it.

Part of me doesn't want to get involved at all. Too much drama, and plus, if I divulge that I know anything, she'll turn it around on me for snooping. Thing is, I'm real close to her and her husband/ family, and it just kills me that she's inching closer to hurting them just to get with some old flame she never got over.

Up until now, a lot of their e-mails have been subtle enough that they're not quite incriminating enough to be "decisive evidence" of what's going on. But yesterday, the other guy sent her an e-mail that, let's just say, would be pretty damning evidence, especially if it got to his wife.

But now I don't know what to do with it... I kinda want to show it to someone involved in all of this, via e-mail; I'd either like my female relative or her "other guy" to see that someone knows what they're doing, and maybe it'd scare them off. But I don't want them to know it's me, so I can't use any of my e-mail accounts. Even if I set up a new one, this "other guy" is kind of computer smart, and I worry he could track this new e-mail account to me somehow, and I'd be outed anyway...

On the other hand, I'd like to forward this e-mail to this other guy's wife, so she can see what her husband is doing. Aside from the same e-mail problem (that is, me wanting to remain anonymous), I don't know how to get in contact with her, and I don't know how to guarantee she'd read an e-mail from a stranger.

I know my plans here are pretty silly, but I just can't figure out how else to drop this big bomb of evidence I have, without making it known that I've been snooping this whole time.