Take a look over your relationships in the past. Have you always held yourself a little bit aloof, even in your most intimate affairs, refusing to let your lover get to know you at the deepest level? Consciously or not, you're a little bit afraid of letting the other person in.
If this is an unconscious feeling, you might see it manifested in repeated relationships with people who make you uncomfortable by being overly intense with you, pushing your boundaries in a way that you don't always like. You might get into major power struggles with them, trying to prove that you answer only to yourself -- which, ultimately, could lead to the end of the affair. If this has happened before, take it as a sign that you're subconsciously attracted to this type of person for the very reasons that, consciously, you're almost repelled by them! This type of relationship offers you an experience that you can either continue to repeat or start to learn from. After all, intimate relationships are an excellent opportunity for personal growth, and one of your lessons is to learn the difference between genuine personal freedom and letting your lover control your life -- or fighting against that possibility.