Help me with the plot of this fiction story I am writing?

Gabe realizes he was the killer of Autumn and tells rachel. Gabe flips out. gabe shoots himself cause he knows he cant be forgiven. after his death, rachel starts investigating autumn death and realizes there was no record of such an event

or you could end it like "and gabe woke up and realized it was all just a dream" haha yeah right

Sounds like fun. You could have Gabe eventually diagnosed with schizophrenia (which you are already laying out in the beginning with the voices and depression) but he was driven to this by an article he saw in the paper about a girl named Autumn. That way, Autumn is a real, murdered girl that be begins to obsess over, maybe as a way to get back at his cheating girlfriend. Hey, dead people never leave you. Actually, you have the makings of a pretty deep psychological story.

Guess after his suicide attempt, have some doctor put him on his medication so he stops hearing the voices, but maybe have Autumn seem to leave him a more concrete clue that could be interpreted either has having actually been left by a spirit or it could just be Gabe putting meaning to something random. Anyway, Rachel will eventually realize that this suicidal nutcase isn't for her, so the reconciliation may have to be a "Friends only" scenario.

I'll try :D

Gabe hears a voice after a short argument with Rachel. It says in an innocent tone, "Hi. I'm Autumn. Who are you?"

He hears the voice which tells him to follow certain trails (like go to the cemetry where the girl's buried)

He speaks (not so often) with the voice and so when he does, these are the special moments of the book. Every now and then, the voice discloses (or lets slip) a piece of information which leads to the logical understanding that Justin is the murderer.

All this time he is having a hard (and sometimes sexy) time with Rachel. The mood within the relationship changes slightly, becoming more frequent in the middle of the story, finally swinging from "perfect" to "terrible". This creates a sub-plot.

The voice gets stronger toward the end, taking up a tone of aggression toward anyone Gabe meets. All this affects his life with Rachel, at work, with mates, and with himself.

Then something happend (or he imagines it) between Rachel and Justin. So he kills Justin. But the voice has taken control of him now, and he is not satisfied.

Here you can decide: 1)he takes his own life after a final departing scene from Rachel - Rachel lives on with this memory, Maybe its her telling the story as she believed it. 2)he takes Rachel's life based on the voice which has overtaken him completely. Then, he comes to himself; this is because of a sudden remembrance of his time with Rachel (a kiss, making love, etc.) and as his mind focuses on "love", the voice is silenced. In that brief moment, Gabe kills himself "in order to prevent himself from bringing harm to mankind." This has a noble touch to its end.

At the end of the 2nd version, you can add that another guy/girl somewhere else was angry at a partner, suddenly he/she hears a voice, innocently saying, "Hi. my name is Autumn, who are you?"

Gabe should find an old grave plot with the name Autumn (Last name should be the same as Rachel's male friend) and come to find out, the male friend had a sister, baby, etc etc....oh and maybe the voices could convince him to dig up the grave....revealing something shocking.....maybe the body of Rachel, meaning who he thought was his girlfriend is someone else

Yes MPD is interesting. Or both Rachel and Autumn are imaginary. Justin is someone he knows like a neighbor or a guy from school who is unaware of what is going on.

Only YOU can perfectly decide a plot (and good luck, you've got a killer on your hands :D)

May I dare to suggest that the voices have Multiple Personality Disorder? Or is that too rediculous?

Boy gets girl, boy loses girl

i am a crappy writer, but what you've got is pretty interesting