What's likely going on is that you have a fear of losing yourself in the relationship. And the more you like the person, the bigger your fear of engulfment and commitment gets. Why? There are a number of reasons you might fear losing yourself in a relationship.
In the end, fear is fear, and we either accept the task of working with it consciously and diligently or we walk away from loving, solid relationships with the erroneous belief that "It just didn't feel right. If it was right, I wouldn't have to work so hard."