Dear Mikaela,
If donating your kidney helps you stop smoking for the rest of your life it would mean two lives were extended from the donation - both yours and your husbands.
It is certainly very hard to stop smoking, but it does get easier over time, and many people do stop completely. If you already have 3 months without smoking, why would you want to lose all that hard work by smoking now? Within another few months the cravings should be less, and you will be much healthier. Plus you will save a lot of money that would go to cigarettes.
Love, elephant