I tell my wife the truth on purchase costs because we both work full time and our income is ours, not just hers or mine. Having said that, I have been known to set up an aquarium while she is out of town! But I owned a local fish store (that is now a pet supply shop) and have about 75 empty tanks left and most equipment needed so flora and fauna is mostly all I have to pay for out of pocket. My situation is different than it ever was in previous relationships. My wife simply does not have expensive hobbies, a love of shoes and handbags, or much of anything that costs much money. I love target shooting, archery, aquariums, gardening, houseplants, and cooking. All at rather high levels -at least in terms of what I think I need. With former long term live-in girlfriends we had agreements that either we use our own money for our expenses, or talked about it and came to compromises. Now I'm with someone who paints and draws, hikes and bikes, and bakes bread and desserts. Most of her clothes come from Goodwill. The amount of $ I need each month is year's worth of her activities' costs. This is partly why I put a ring on it though to be perfectly honest!
Nothing good happens fast in an ecosystem.