Quoted from ShinyBall:
well, when you are talking about spending 8k to 10k..I think both need to agree..at least in my household.
I would agree with that sentiment 100%.
(I should say up front that in our family, the hobby money is separate, and the living space is mutually funded/shared/enjoyed.)
In general, I just prefer a different approach than 'asking for permission' to reach agreement on any subject with my GF. In short, I ask her opinion to see if she thinks doing X is a wise decision. She considers it thoughtfully from a few angles, and gives me her honest opinion -- I don't always like what I hear, but her considerations always help me make my decision. I just put the shoe on the other foot and think -- Hey, I appreciate being asked questions about her tougher decisions to make (she makes most of them alone, and doesn't need any outside input), and so I try to include her in the process of making mine when I can.
As a teenager, I asked my parents frequently for permission, since they were in power at that time. It would be out of character for me and my GF if were asking each other for permission on stuff. For us, that might feel more like a hostage crisis standoff -- a power struggle. Every family is different.