If it is on you mind why not go ahead and tell him about it. My husband has never been one to care about how our money gets spent. If he wants something specific then we decide if we can afford it. When I inherited a rather large some of money I bought him a set of drums for his birthday. It was around $8,000.00. I had been wanting a new good machine and went looking, ended up buying a $2,000.00 machine, table and a few accessories. Felt rather silly about spending so much since I had 2 good machines but nothing that would do any fancy stitches. He thought it was great that I would spend money on myself. I had no trouble spending it on him and our 2 daughters - but second guess spending much on me. Then there was the incident of buying 3 featherweights within 2 weeks when I didn't know how to remove a bid on ShopGoodwill.com and Ebay. Luckily I got them for very good prices, I was so thrilled to get the first one and hoped I would get outbid on the other 2, but didn't. Was hoping my daughters would each take one - but neither one wants one. So taking one to WA for my sister in June.
So as long as the rest of your family is not suffering from spending the extra money, he will more than likely laugh over the bobbin fiasco and realize you now have another back-up. Or use it for a trade in later when you are ready for an up-grade.