You don’t. You do what the rest of us do and hide it away from our loved ones at all costs. They must never know… ever. :-X
Seriously though, it’s your money so do what you want with it. If your missus starts giving you grief because you want to spend a small bit of your own hard earned money on something you love, then I’d say start looking for a new girlfriend to match your new yoyo. 
Trust me, the yoyo buying addiction is only going to get worse from here, so she had better get used to it now. This is just how it begins, give it 6 months and you’ll be working double shifts and a night job just to pay for your 12th Draupnir.
Speaking of which… I wonder if they’re back in stock in any new colours…