You're a fighter, a warrior. You didn't choose this battle but you have to choose to fight. Better days, better moments will come. Bad days, worse moments will come too.
Find good reasons to stay, write them down, recite them, remember them. You were given life and are worthy of life. Pain doesn't give any of us a break.
Find a purpose to deeply believe in. I believe we have a responsibility to the world; we have higher purpose that we will never fully realize on this physical plane. Fight defeat with faith. Keep fighting. The world is full of lies and constantly feeds them to us to hinder our purpose and steal our joy. And there's more to this life than what we can see with our eyes.
You live to fight another day... count it as a victory, no matter how sad and defeated you feel, you have inner power that you need to learn to recognize and encourage.
Pain spares none of us. You're a warrior! Never forget the power and purpose that you have.
Oh, and most importantly:
YOU ARE IMPORTANT!!