Let's not jump to conclusions. There are other reasons he might be reacting negatively to your question.

It's human to expect the worst. And the worst scenarios always involve our greatest fears and insecurities. I know it's hard not to react emotionally when it comes to the opinions, attitudes and potential actions of people you love, but try. Take a moment, and find your inner-robot. Let's be rational here. Non-emotional. Fear is like a vampire -- it has to be invited in. So keep it out on the porch.

Your boyfriend could possibly be sick of the question. Try to think back: did you ever ask him about his past, and did he politely say, "I don't want to talk about it?" And then you asked again a few days later and he said, "I still don't want to talk about!" Then you waited a day, and asked again, and he was all, "RAGERAGERAGE?"

Maybe he thinks you're trying to trap him. I know from experience, sometimes women ask loaded questions of their boyfriends in an attempt to "trap" them. Everyone has a haunted heart. If you've ever shared yourself with someone, they'll always be there inside of you. Faint, and distant. But they are there. That's healthy. What isn't healthy is a jealous significant other coming at you with a pick axe, hellbent on finding proof that you existed before the two of you met.

He probably doesn't want to talk about his ex because he is with you. It's really easy to judge someone by what they say or don't say. Because words sparkle. But you should judge a person by their actions. What they do. Which is boring. He is your boyfriend? Is he a good boyfriend? Does he do the things a man should do in order to show a woman that she is important to him? If he does, then what else matters?

It could be that he deeply loathes his ex. Or regrets treating her poorly. Hey, he could still have feelings for her, but you can't control his thoughts. Nor do you want to. Right? Because if you do, maybe you should date your DVR, as human beings don't come with remote controls. Consider this: he might not actually care about or even think about his ex. He could be frustrated that you keeping bringing up something that doesn't matter to him. It only matters to you.

Being afraid or insecure is a choice. Don't make either of those choices.