I'm going to lose interest in a girl because of her dead boyfriend
What about the dead boyfriend is making you lose interest in her?
I'm too jealous when I hear her talk about him.
Your girlfriend had a relationship before you, it is understandable that she would still think about her dead boyfriend sometimes. Try to be sensitive and not think of him as competition.
I'm kind of a jerk like that, but I can change.
There is nothing to be jealous about as your girlfriend loves you. I know that you can change the way you handle this, so trust in yourself.