Writing a book, the main character is a girl, 16, there's a lot of other details but the main plot is that she develops feelings for a new guy in town (it's set in an old western town), but it turns out the guy is a machine that has been made specifically to cause her death, although he has been programmed not to kill her directly. Through a lot of pain and distress he causes her to commit suicide. It's goes on to be slightly more complex and I have a lot more planned out but I was wondering about this bit ? If you want to know some more of the details please say.
All ideas are worth investing in if you're invested in them. Ideas don't have to sound good, excellent or dumb - the outcome will define that. If you love the idea - go for it.
I think that's were the cyborg type thing came from but he's definitly not as cool as the Terminator. My guy doesn't recall when he kills he blanks out. The people that made him used his being to disguise the machine/cyborg. So the guy still thinks he's alive and not made of wire and metal. I kinda got that idea from an episode of Doctor Who.
Reminds me of Terminator, as well. One thing I think you'll have to explain very well is why the robot can't kill her directly. That seems pretty far-fetched. It's fine if there's a good reason for it, though, so I hope you have one!
I instantly thought of Terminator as well. But, the idea sounds interesting enough. I agree with Minstrel though, you will need a good reason for why the robot can't kill her himself.
A story concept means nothing. What matters is how you write it: the characterization, the flow, the imagery, all of it. There's absolutely no benefit in asking what other people think of the concept! They'll either say,"Sounds great," or, "it sounds like a ripoff of..." If the idea stirs you, write it. Then ask people what they think of the final story. After they tell you what they don't like about it, revise it, usually several times, until you're happy with it or until you throw up your hands and say the hell with it. Only you can decide if it's worth developing. How much time and effort are you willing to put into turning it from an idea to a fully-developed story. Please read What is Plot Creation and Development?