We all have the tendency to fall into old, unconscious ways of interacting when making our way through a relationship. That's just a natural part of being a human being. But that tendency is avoidable in this relationship.
You probably felt comfortable together right off -- your bond felt natural, familiar, as if you'd already been a couple for a long time or even as if you two had done it all before, together. This is certainly a possibility. An even greater possibility is that you are both reenacting past relationships from this life -- revisiting feelings experienced either with your parents or with significant lovers from your past. Why is that a problem? Because it could mean that your growth will be stagnant in this relationship, if you're just acting out an old one. There isn't room to grow within a relationship unless you're able to truly be yourself as an individual, and to see your lover as their own person as well. Furthermore, you could be reenacting past relationships that weren't good for you the first time around, much less this time. You should both take care to examine your bond closely and make sure that you're interacting as individuals in the present rather than carbon-copy figures from the past.