Can't we all be friends?

Last weekend, one of my gamers invited a friend (I'll refer to him as Rex here) to come by and observe our nWoD game, as Rex was trying to learn the sytem and had some questions about how to run a game. I'd already been made aware of this, and it was fine by me.

However, it turned out that Rex was not only known by my other gamers, but he'd been the center of a fallout between one of my female gamers (I'll call her Stephanie here) and her best friend/former gamer in my group. Stephanie's boyfriend was also in my group as well.

When Stephanie found out that Rex was coming to the game, she was afraid he was coming to deliberately ruin her night and, in tears, refused to come to the game while he was present.

I didn't find this out until the irate boyfriend showed and asked to speak with Rex outside. Next thing I know, I'm hearing shouting and threats from outside. I'm on the verge of going on outside to try and possibly break this up, when Rex comes back in, apoligizes and hastily leaves.

I then get an expination from Stephanie's boyfriend of what's going on, and that he's going back to try and calm Stephanie down and coax her back to the game. At this point I'm flustered, embarrassed and hoping Stephanie will be okay. Stephanies boyfriend leaves, but I later get a text they won't make the game that night, she's still too upset.

And the more I think about it, the madder I'm getting how the whole thing was handled. I really feel like Stephanie overreacted, and I surely don't appreciate Stephanie's boyfriend coming by just to make a scene, and then threaten a guest at MY house and leaving my other gaming friend embarrassed for bringing someone by. I beleive I'm going to be having a discussion at the very least with Stephanie's boyfriend on our next gaming night about the whole situation.

Had any similar game group issues that have left an impression on ya?