Am I wrong for wanting to know his past?

So my boyfriend was previously married. However, he avoids talking about his past marriage. I don't care about his past but I just wanna know what went wrong so I make sure the same scenario won't happen again. My main point is to learn from mistakes to make ours succeed but he gets so mad when I mention it or ask him questions. Am I wrong for wanting to understand what went wrong in his previous marriage?

I'm even considering contacting his ex wife and asking her. I started feeling that he is hiding something serious