Well, I think that when a guy wants to enter into a relationship with a girl, he wants to make sure that she doesn't have a bad reputation and he also wants to make sure that she never dated anyone he may know or be friends with.
Although this may seam shallow, it is normal for us to have a basic interest in your past but not so much that it dominates every conversation. If a man becomes obsessed, that's a red flag and you should get out of that relationship!
If there is to be true love then the past really shouldn't matter. I dated a girl in my early teens and I soon found out that she had quite a reputation-she had even been with my cousin and a lot of our friends. Once I found this out, it was uncomfortable to say the least and I had difficulty in accepting this. Over time, however, I was able to forget and move on in our relationship.
In short, it is normal for guys (and girls) to have such an interest (Would you buy a car without checking the mileage?). As long as both people are honest-and willing to accept the answer to the question they are asking-and no one becomes obsessed abut it, then they should be able to move beyond the past and into the future.