You are severely
underestimating yourself, in a variety of ways.
You are underestimating the impact you make on people's lives, and how much pain you will cause by the action: A few days ago, as I was just getting into everything2, I discovered that Hermetic killed himself approximately a year and a month before. I broke down crying for someone I never knew. If you kill yourself, the effects will ripple through all the world.
You are underestimating your own strength and coping abilities: no pain cannot be endured. This is not meant to trivialize what you are going through. I understand that there is emotional pain that consumes everything, and I know that I would not want to endure it. However, your pain is only a feeling, and if you don't give in to it, it will make no difference.
You are underestimating your ability to change: as long as you remain alive your circumstances can change. If you are lucky, this may not require any active attempts on your part. However, if you do make an effort to change things, they surely will. Perhaps not at first, but things will get better.
Finally, you are underestimating your worth as a person: All people are valuable in some respect, and every last one of them is too important to be thrown away. This is the reason that suicide and murder are illegal in the first place. If you sit and think about yourself, and ponder what good qualities you have, you will see that you are too valuable to throw away, no matter the reason.