Killing is not a good thing in my opinion (I'm guilty for saying this). But really, revenge is not the best option in my opinion over all. You're strong for what you've been through, but really is it worth it? You're just going to put yourself lower then him, showing you're no better and all. And honestly it's ok to feel bad over thinking that, you did think it because he did cause you a damage you will take for the rest of your life. As well its not your fault for thinking, when people feel anger we tend to always think of a way of discounting. And it's ok, but we all need to learn how to become better right? I can guarantee, hes not important in your life anymore. He's far far gone, he's just a memory now and that's how you should see him. It can hurt, it can be hard and painful to just let go of all of this. But you will do it, one day you will probably look back and be proud of how strong you are and how you can always keep moving forward no matter the situation