The reality is that a Kelly is a MEGA expensive bag, lol! I'm a college student, and I'm 22 years old, and there is NO WAY IN FREAKING HELL I will EVER let my parents know about the price of my future Bolide or they would crap their pants and probably wack me upside the head. They just do not spend $$$ money on luxury items, even though they have it to spend; they buy antiques and jewelry, and nowhere within their reasoning sits a $6,000 bag
It really sucks that your AHEM ARTARD/DOUCHEBAG AHEM boyfriend decided to tell your mom. And it sucks that your mom didn't take it well.
But it's just a bag. And you're 19 years old. And you will definitely, without a doubt, find a bag you probably love even more later on. A bag is just not worth your relationship with your mom. Material goods do not come over family, no matter how delicious the smell of the leather and how hot it looks with what you're wearing.
Sell it, buy yourself something fun in ***secret*** that isn't quite so expensive, and I highly recommend finding a very sweet, pale, intelligent nerdy boy (the best kind on earth), as they tend to be very accepting of your every crazy whim and have no issue with assisting you in your purchasing dreams
Though no one seems to ever understand this...lol! My sweet nerdy boy knows all things that make me happy come in an Orange box
At any rate, you can be the most mature lady on earth and your mother still won't like you owning such a pricey bag, at least for now. Hell she may never like it. And I know there are ways to deal with this in such a manner that you might be able to weasel your way into keeping the bag. But in my humble lil opinion, making a purchase like this should be one made in not only good conscious, but one made without trouble or freaking out mothers attached to it.
If you can't enjoy it to it's fullest, without people rarrrring at your neck over it, it just plain isn't as much fun.
Think about it this way: if you get the $4,000 back, and save it, in a year or two you'll probably have enough for a brand spanking new color-of-your-choice Kelly, a Birkin, or hell maybe even TWO used bags!!! And once you're out of your mom's house, you can buy a GREAT bag in good conscious, without someone waiting to ruin your happiness by trying to make you return it.
I hope everything works out for you ^_^