Glad you had a good weekend, Moridin
About your wife hanging out with "that guy" on spring break, ugh
Tough call.
When I first found out about my ex's mistress, I completely forbid my husband to contact her at all for any reason. In fact, we were supposed to help her move out of *her* husband's home just a few days after I found out that my husband was one of the reasons she was so eager to dump her husband. Obviously we didn't help her move after that.
I'm not so sure that restricting my husband's interaction with this woman was a great idea on my part, in hindsight. First off, they still saw each other at work every day (so did I, since the slut was my boss - I worked there part-time). After his mistress managed to get me laid off from my job, I no longer had "supervision" of my husband during work hours.
It seemed that my restricting contact between the two seemed to intensify their relationship - as if the "forbidden fruit" was much sweeter than before
So - putting the locks down on your wife might not be the best idea.
However, I'm a bit dissapointed on your behalf that she would even consider traveling anywhere (even in a group) with that guy. I would hope that she would refuse to do that, out of respect for your feelings, and as a gesture towards you that she is working to be again worthy of your trust.
What does your therapist have to say about this little trip of hers? Did the therapist offer any advice as to whether she should go or not?