You find that there is a highly subtle bond between you that just can't be defined. You feel attracted to one another on a deeply emotional level, and probably have from the very beginning; but at the same time, you both sense that things just aren't quite on track between you. Something deep and important is missing, and until you're able to pinpoint it -- no easy task -- it bothers both of you, but especially you, perhaps to the detriment of the relationship.
This subtle problem is related in part to the fact that you communicate both verbally and nonverbally, and the nonverbal communication between you is tense. It's as if you're each sending out mixed signals. Your lover might be transmitting a very real feeling of coldness or frustration that causes you to react by pulling away, and in turn, they feel the distance...and so it proceeds. Then, when you're sharing a moment of warmth and intimacy, you're wondering, Is this person being completely honest with me? Can I really trust their feelings for me? Somehow, they're unable to make you believe the truth of their feelings. It could actually be due to the fact that their feelings for you fluctuate frequently, or yours do toward them. The only way to deal with this is to wait and see what develops between you. You may find that your bond is deep and true, or you may find that you just don't make a good match.