Fiancé bah! She's not your wife, that's when you have to worry about bringing bikes home haha. There is no saying "happy fiancé,happy life"...
Around our house as long as I don't touch the joint bank account, I spend my own money on whatever I want and the same goes for my wife. We got a good system going, I'm lucky. She rides motorcycles to so there's never a complaint if I buy bikes, in fact shes talked me I to buying one ;p