You both have a hard time feeling safe and supported in this relationship, and you aren't able able to figure out why. After all, you are both looking for the same things, on the surface -- a close connection, a feeling of togetherness. But somehow, you just aren't able to connect on that level.
If other aspects between you are more harmonious, you are able to make a good, strong connection, but there is still this feeling underneath, gnawing away at you, that something's not quite in place. Feelings like these are almost always carried over from a past life. In some other realm, you were involved with each other in a contentious way. You may have been rivals of some kind, or you may have been lovers who betrayed each other. In this life, there are still threads of that old feeling of mistrust running between you, and it is hard to ignore them, even if other things are wonderfully in place between you. If you want this to last, you may want to try to ignore those feelings -- and you definitely want to communicate your trustworthiness to each other on a frequent basis. Even if it seems like it should be obvious, go ahead and tell each other that you're in this for good reasons; that you can be relied on. Then live by that code. It will go a long way toward resolving old, past life feelings of mistrust.