Moving forward into your future is a sign that you're progressing as a human being. To stay focused on the past would be to stagnate or even regress, and unfortunately, the two of you together could spend more time looking backward than forward. This person doesn't mean to hold you back, of course, but they're very focused on your past, which could ultimately be a hindrance.
It could even come from a good place -- maybe you had similar upbringings, and you enjoy comparing notes, or maybe they try to help you get through an emotional problem by taking a close look at where it originated. These are wonderful connections to make, but you can't stop there! If there are problems in the relationship, looking to your pasts for the answer is only one part of the solution. You should concern yourselves more with where you're going, both as a couple and as individuals, especially if one or both of you has had a troubled past. Moving on is the only way to, well, move on! And if you insist on inspecting the cracks in the sidewalk of your life, you don't get anywhere together. Don't let your partner put you through this. Instead, turn your focus toward the future. What direction does each of you need to move in to improve your lives? This is the question you need to ask yourself. And if the answer leads you in similar directions, so much the better.