There are three usual responses to your predicament:
1. Look on the bright side!
2. Well, polar bear cubs are cute and things, so you should LIVE TO EXPERIENCE THE NATURAL WORLD.
3. WELCOME TO THE ATHEISTS' CLUB! Coats on the left, drinks on the right... We've got cake and punch and reason-derived moral codes! You'll love it!
The responses you should give to the first two, are, respectively, hitting them, and, "oh, f*** off, Attenborough"- possibly whilst hitting them. I humbly offer the third.
First: depression lies to you. Sonofabitch lies through its teeth, and on NO account should you trust it. The idea that the lack of a god means your life is not worth living SEEMS logical to you now, I'm sure, and you're looking now for logical counterarguments. This is completely the wrong approach to take. You will never defeat depression using logic. You can hit it with as many rational arguments as you like, but it will not back down or fade or admit defeat to any force other than time. This is what the ****er does: it takes your rational thought and twists it and poisons it and presents it to you as reason. It's made of the fabric of your own mind- that's why it's so hard to defeat.
Here are the logical counterarguments to the idea that life is not worth living: your life does not have meaning in the sense that it is a word in the language some god uses to communicate with itself. Your life is its own meaning. There is no higher force or power, so your own joy and pleasure is the most powerful, complex, divine force in the universe. Your pain and heartbreak is its greatest tragedy. Your existence in the face of the bleakness of the empty universe is a brilliant, miraculous triumph over a hundred different calculations that say you should not exist. You are the universe's happy ending, its deus ex machina. Every fibre of intelligence and beauty in existence lives and dies in the genius clockwork of your body and mind.
You won't think this is enough. You will present this to the embedded truth in your head that life is worthless and it will remain, stubbornly, undislodged. Like I said: you can't defeat it with logic. You have to hold on to your life and hope, unfailingly, relentlessly, even in the face of a hundred different thoughts saying you shouldn't, until this passes.
And it will pass. Believe me. The world will not always look like this to you. One day, I promise, you will fall in love and it will be joy purer than any beauty the natural world can hope to produce and you will look back on every thought that ever pained you and know that it would be worth enduring them a thousand times again so long as you lived to feel this.