A word of financial advice (as I used to be a financial advisor), if you can't afford to buy it with cash, then you can't afford to buy it on credit.
As for getting "nothing" for a Nikon after three years of use, that probably isn't true. You can get a Nikon D800 for less than half the cost of an M9, and the Nikon is a superior camera in every way. A D800 will probably not depreciate at a greater percentage than an M9 over the next three years, though it probably will after 4 or 5.
Don't "lust" after gear. Get what you need when you can afford it. Many pros simply rent what they need for a particular gig (professional photography is not a particularly high-paying career). Relatively few professionals shoot with Leica equipment, partly because of the high price, and partly from it's limitations.
Most Leica shooters are people with higher disposable incomes (money left over after paying all one's expenses). At 22 you are not likely to be one of these, and if you aren't careful with your spending, you may never be.