1) Your brain cannot die. If you killed yourself, you would be even more obsessed with whatever it is that is troubling you now enough to make you talk this way. You think that whatever it is bothers you now? Then imagine having to live through an eternity full of nothing but these thoughts obsessing your never-again-sleeping mind!
2) Without a body you would be powerless to improve your situation. Here is a fine mess! Post-suicide, all the problems remain - the only difference is that now you lack the means to do anything about them. You lack the power to do anything about anything! And the act is irreversible. You can never say, "Whoopsie! My bad" and get your body back.
3) You would suffer a life review in which you would get to suffer all the pain that your act had inflicted on your loved ones. And not only that, but you would feel the suffering and loss of your planned future wife, your planned future children, the eternal friends in whose lives your future self would have been a powerful force for growth, and all the big and little ways in which your stupid, selfish, pointless act had harmed other people that you don't yet know.
Stop it now. I can recall being a teenager, too, and actually even flirting with the idea of suicide as a kind of adventure - what the heck. At your age, people feel invulnerable and immortal. The notion that any impulsive act could be irreversible and might leave you with an eternity of nothing to do but suffer an awful, wrenching regret never enters a 17-year-old's mind. It's time to grow up now, dear friend. Listen to Brett, and listen to all the others here who love you. Suicide is never part of anyone's life-plan, nor is it anybody's destiny. Your long and beautiful life is only beginning!