Twice I've had to deal with my main squeeze having a first overnight. Both times it was the unexpected that threw me.
The first guy, it was a 2nd date (first date at his place) and she stayed out all night unexpectedly! Her phone died and she was there too late to catch the last bus across town, and she was too shy to ask to borrow his phone or computer to let me know. And to boot, it was Halloween and I was worried she was attacked by some drunken revelers. I sure read her the riot act when she got home. I was frantic with worry mixed with jealousy.
The next time, different guy, she asked if I'd be ok with her going to this guy's gf's photo shoot (she's a fetish model). Of course I said, sure, no problem. She neglected to tell me the shoot was in Maine and involved 2 overnights with this couple and several of their friends, party atmosphere. She told him I'd given the OK, and THEN she told me it was a whole weekend thing.
When I found this out, I didn't want to be a bitch and say, oh, you can't go then. So... I spent all of the first day she was away masturbating! Yes, 12 hours, only taking breaks for food and water and a short nap. hehe. It was kinda fun, and definitely distracting, but probably doesn't work for most people.
Soon after that I met her new squeeze and his gf and then I was fine with her going away on one or 2 long weekends with them. I find once I meet the new person they seem like a friend and not a threat to our relationship.
Like NYCindie, I also ask if you and your wife never go on trips separately, on business, to see a friend or family? If not, now is the time to start, so that your brain might be tricked, when she's with a lover, that she's just away having fun with a friend, and will have interesting stories to tell you when she gets back!