Yes, obviously I mean the only reason I would want to die is because I want to know what happens after death, but other then that I prefer to stay alive. I don't care if everybody I care for dies. I mean, science will eventually find a way to make people stop aging, so yeah.

How I don't want to

If you were trying to say: "The way/in what manner I don't want to--- do something", the sentence is better if you clear WHO is the subject of the sentence (YOU are the person who does not want to do something). So to make things short, put an "I" before the "don't".

I'm not sure if you are trying to say something like that, because I don't see the relation of that with the text below (in the text you are saying "reasons which make me wish to die", and you don't talk of "something you don't want to do", like in the title, so it doesn't make much sense).

Also, maybe you were trying to say "the reason I don't want to do something", so in that case "why" instead of "who" is better (I'm suggesting this, because it isn't so common to find something like "How I want to/don't want to", but is is more common for someone to explain the reason behind their wants, like "Why I don't want to do this").

Yes, obviously I mean the only reason I would want to die, is because I want to know what happens after death o. Other thean that, I prefer to stay alive. I don't care if everybody I care for die, I mean, science will eventually find a way to make people stop aging so, yeah...

1- the verb "happen" has to be used in "present simple", so you have to put an "s" at the end of it; "happens".

2-You are saying a lot of things to fit them all in just one sentence!
It's better if you try to put a rule, to just include 2 or 3 actions (verbs) most in every sentence. Also, if you put commas in some places the sound is overall better! [maybe the commas and where you should place them are a bit more of a problem- you could try to think, where would you make a pause, in the same sentence, when you are speaking? Think that normally, you wouldn't say so many things without a pause :) !]