youthtoday

I think your first point has a lot of merit, not necessarily the second. She should have chosen another night to go out, she obviously knew about the camping trip as your son had been talking about it for two weeks -- I doubt she forgot. But if you trust your wife and she trusts you, there's no need to worry about what she was doing. She was out with girlfriends. Making a big deal about that part and implying she was cheating is going to make a bad situation a whole lot worse and she'll think that's the primary reason you're angry.

She needed to hold down the fort while you had bonding time with your son and it's not unreasonable to ask her not to do that in the future.