All three of you are incredible, wonderful, collections of atoms, the chances of whose formation and resultant animation may have been a brilliant fluke in a huge universe.
Your years are 120 or less, and then the universe will reclaim you as its own. For the universe, the span of your life should have been not even the fluttering of an eyelash before a blink. From a cosmic perspective, the existence of our whole galaxy was set to be one giant quantum fluctuation - the birth and death of a mere grain of matter, falling from one eon to another.
But then something incredible, something unexplainable, happened. Inanimate matter came forth from the deep waters. It grew legs, it started to paint on cave walls, not yet aware of the implications of what it was doing. (Have you ever wondered - of all the things the most significant cluster of particles in the whole universe could do, why would they choose to paint?) We started to reproduce. We started to communicate, to love, to build, to live! There is nothing else like us in the vast cosmos, and there may never be again.
The Milky Way should have be one passing glow of light, but somehow this humble galaxy became greater than the remainder of creation. The wondrous flash of light as our galaxy passes through existence will be most glorious moment that the universe ever experiences. You alone - a lonely sentient creature - would be that blinding flash of light even if the rest of us had never existed. The wonder of you, even as you contemplated an end to your solitary existence, would fill space long after every sun died and time itself drew to an end. In such a universe, you alone would have been notable. The fact of your existence is more incredible than the largest sun or the most massive black hole. Your glory - the glory of us all - will fill the universe forever, a single proud memory in the vast emptiness of space.
We tend to take our existence for granted, but it is an incredible fact - a miracle which all the religions on Earth were born, or given to us, in order to explain. Who would have thought? Who could have guessed that this tiny backwater planet on a spiral arm of the Milky Way would end up defining the vast cosmos forever?
Now, here is the important part: All the dead matter in the cosmos - every particle of the sun, the galaxy, and the vast everything - would give it up to be you. Sagittarius A* would disappear in an instant, if it could change places. It would give 13.2 billion years of existence for your measly 120 years of life.
Your life, unfortunately, will some day draw to an end. You know that, your atoms know that. Perhaps you are tempted to end it earlier, but no mistake could be more grave. I know not what you believe, but even if there is heaven or hell, there wont be anything like now. Let your atoms live. They have eternity itself to be inanimate.
A handful of misfiring neurons has no right to bring you to an end. The world is blinding. If your neurons can't see, you must do everything you can to fix them. Depression has easy medical fixes. Being treated for depression, fixing such a tiny flaw, may be the hardest challenge you ever face - but it is minor in the grand perspective.
Lastly, I leave the cosmos behind and appeal to you. Whoever you are, however you came into existence, and no matter what your purpose is, you are capable of understanding deep philosophical arguments and complex equations. I have none of that for you, merely a saying often heard on HN or in rejection therapy groups: Never say no. Ask yourself what is necessary to make life worth it. If you need a vacation to Hawaii to make life enjoyable again, take the next plane to Hawaii. If you cannot live in a meaningless world, leave for the mountains of India, where you may seek enlightenment in silence among fellow travelers in the sanctity of a Buddhist monastery. The parent posts' comment on marijuana is right on, but free will can do more than justify life - it can make it as brilliant and wonderful as you desire. The universe envies your ability to choose.
Before I end, I want to point out that all of you left comments here instead of suffering in silence. You are already ahead of the game. You can email me at aantny@gmail.com anytime. If you email me or call me on Skype, you would be helping me take a break from schoolwork to discuss philosophy. If you're in Israel, I would love to meet a fellow HNer in person.
You are brilliant. You are incredible. No matter your flaws, your crimes, your inabilities, I would kiss you. I would hug you. I would bring you into my house and eat with you, only to hear you speak, to hear your stories and your laugh. It may not always feel so, but you are a wonderful, beautiful creature. Love yourself, so that we may too.