Wow, Sky. That's just $h!!ty, and after all you 2 have been through...
As Mr 5.0 said, you have my empathy. I just hate hearing about this stuff going on. What the F*** ever happened to being faithful? Are we just old fashioned? Is everyone else raised wrong?
Sky, judging by what you've put up here on the 'boards over the years, I think you're a pretty cool person. I just hope you know this, and don't bang your head against the wall for what's happened. I've been in that relationship where you've known each other since teens, then you're stuck out in the "real world," and everything changes.
Sky, I'm willing to bet she's going to get burned by this dude, and may even come back to you. So on that note, just keep your cool, K? I know exactly what you wanna do, and I feel ya on wanting to beat his ass/scare him!
On the upside, this happened now and not 5-6 yrs into a marriage. I have friends from high school I graduated with that have gone down that road. These days, being single and still going to college, I look back at that time in my life, and I'm happy that it happened the way it did. It made me a better person just being with my high school GF, and I found things in myself that I never knew about. I will still always wonder what would've been, but I don't dwell on it. I just thank God for the time He gave us together, and move forward with my oh-so-crazy life.
I only hope you find something like that on your own path, dude.
Here's to you, Sky.
Good luck and keep your head up.