Why do I enjoy thinking about death and murder so much?

I've been depressed pretty much all the time when I was 13-18. At 18 I started seriously considering suicide. Then I fell in love and had the happiest time of my life, then I lost it. I started feeling not so much depressed anymore but enraged, first at my ex, then at the whole world. I can't count the number of times I've played different scenarios of killing her and her new boyfriend. When see a death or murder on TV, it doesn't disgust me anymore but kind of satisfies me a little. Am I turning into psychopath because of what she did to me? Or what caused me to become like this? Ever since she left me I've become a TOTALLY different person. It's like I really did finally commit suicide and now I am reborn into someone else, but instead of being unsatisfied with myself, I seem to be unsatisfied with the world. And I stopped making attempts to talk to people and find friends, not to mention find a girlfriend. I hate people, their big homes and cars, their happy families and kids.