If you have separate finances and can afford it then #treatyoself. If you have joint finances then maybe have a discussion about how many bags you realistically want. I think anywhere from 5 to 15 is reasonable. Every working person should reasonably have a business bag, a crossbody bag, a tote bag, a backpack, and a travel bag. Women should also probably have a clutch and/or miniaudere. And then there are SLGs.
The neverfull can take you from the grocery store to the airport, but IMO you really can't use it for formal events, and you may not always want to use a tote depending on what you're doing.
If your husband has an objection to having more than one bag from the
brand then I would suggest getting a clutch from Bottega Veneta, a crossbody from Chanel, a cabin bag from Rimowa or Globetrotter, a backpack from YSL, etc. Variety can be the spice of life.
If he has an objection to having more than one bag
total then you have to explain to him that a bag collection is as utilitarian as a car, and only having one is like having a car with only one tire.
If finances are a concern then building a designer bag collection by getting one every 6 months to a year is totally reasonable to me. Christmas and birthdays are great occasions to ask the DH or to treat yourself, and something to look forward to.
You can prioritize the bags you spend on, too. For example get Samsonite luggage, an unbranded clutch, a Jansport/Eastpak/Fjallraven backpack, a
Coach business bag, etc., so that you can afford your grail bags over time.
IMO $12k on a car purchase is very reasonable if not frugal if that's his only car. But if he bought a second car or spent $12k upgrading (i.e. not servicing) one, that is a luxury, and if he'll spend that in a year, he should understand why you would want to spend $4k+ at LV in a year.