Since this is a completely optional trip (No friend or family member in need and no family event), I think couples SHOULD make these decisions together.
Why? Because it builds a sense of working TOGETHER and creates and strengthens a BOND with a couple.
By discussing and resolving any complications, ie financial or scheduling snafus that might exist ...
Yep that's exactly how I see it being done. That's why I don't think the conversation is finished on this issue for either of them. There is still time for them to resolve the complications. I don't mean that each one has to be perfectly happy and content with the decision but they should feel like the major issues have been heard and dealt with as best as possible.
Well, that seems reasonable to me. Even couples with a healthy independence need to take the spouse's agenda into account when planning trips, especially when there are children at home. The ideal seems to be, "I'm planning to do thus-and-so on these dates (well in advance), does that work ok with your schedule too? Are there any expenses coming up that I need to consider?" And then discuss.
Not, "I'm going here and spending this; bye." But also definitely not any form of "Mother may I? ....."
At the end of the day, it has to be some form of "These are my plans, let's make them work as well as possible for both of us." Supplication is way way toxic.
If she wants to discuss this at greater length, fine. And I can even understand what you say about expenditure recoil; my husband gets that. But to the extent that these are her emotions talking, as opposed to reason ... he should acknowledge her concerns, but not defer to them. If it's not his truth, he shouldn't live his life by it.
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I don't know her background ... but I can't help but wonder how much of this is driven by her insecurities. This whole scenario reminds me powerfully of a friend of mine whose wife is *extremely* resistant ... "make his life a living hell by emotional outbursts/blackmail/all kinds of low drama" resistant to him going anywhere fun with friends, in town or out of town, without her. Even if she's been invited and doesn't want to go. In her case, it seems to be about fear of abandonment.
My advice: Nothing will prove that you can go have fun with your friends on occasion and still come back to her better than if you find the gumption to weather the emotional storm and go and have fun with your friends and then come back to her. He's done it a few times and the world hasn't ended yet.
"Show me a completely smooth operation and I'll show you someone who's covering mistakes. Real boats rock." -- Frank Herbert