For one, I think lying in relationships is counterproductive. I consider it extremely disrespectful to my intelligence (because especially in a close relationship, the truth comes out eventually) and to the purpose of having a relationship in the first place. Isn't the goal to have someone to love you for who you are, shoe addiction and all? It's obviously one thing if you're trying to save for a house, or a new car, or simply to pay off your credit card debt, but if you have the money to buy one, then what does a shirt matter?
I just keep thinking, though, there's no need for deception in the first place. If it's so important for you to consume without regret, it's easy enough to keep your money separate. Several friends of mine do this — you get one joint account from which the bills are paid and contribute to that as you agree, and then keep your own accounts. As long as the mortgage is paid, the 401K is growing and nobody is going into debt on the sly, then her money is hers and his is his and no one complains about the new golf clubs or the new shoes because no one is feeling like they contribute to the joint expenses more than the other, or that their money is feeding the other person's silly spending habits.
Spouses Who Spend And Pretend [Wall Street Journal]