I think about quitting because I am insecure.
Why are you so insecure?
Because I'm jealous of my boyfriends ex-girlfriend.
Don't be so insecure, learn to believe in yourself. Maybe you should talk to someone who can help you get over these insecurities.
I think planning his death while we sleep is a good way to solve the problem.
It would not be a good to solve the problem, it will just cause more problems. You need to talk to him so that you can resolve your feelings and move on with your life.