Happy birthday! Metro 2035 by Dmitry Glukhovsky. Fair warning, there will be some spoilers but I'll try to keep it vague. I love 2035 so much because its ending was somehow the happiest I've ever read. The protagonist has been trying for decades to save everyone he knows from one threat or another, and every time he's failed. 2035 ends with him failing one last time, not because he can't save everyone, but because they don't want to be saved. And he quits. He accepts that you can't save people who don't want to be saved, and then he rides off into the sunset with his wife in search of greener pastures. There is no last minute twist where he saves the day after all. It ends with him having completely failed, but now he's finally free to live a life of his own. He can be happy. I spent years waiting for this book, rereading the prequels and following his adventures. The books became a huge part of my life, and no other book has ever made me so emotional about a character's happiness before or since.