You might never feel completely at ease in this relationship, and that's something you should know at the outset; otherwise, you could get more and more deeply involved and never understand this odd, vague issue between you. You'll sense it more than you'll be able to understand, describe or explain it, because it will exist at a subtle, emotional level: There will be some feeling of secrecy between you, as if your lover is holding themselves apart from you rather than letting you know them as they truly are. Will they be withholding feelings from you, or needs, or judgments, perhaps?
Did they keep secrets from you in a past life in a way that led to betrayal, or a conclusion even worse than that? Either way, in this life, it's not so much what they'll hold back as the fact that they won't allow true, clear and direct intimacy to happen. What to do about this issue? One method will be to stay in the relationship and passively hope for things to clear up someday (they won't), or you could push for clearer communication -- which may have positive results, though it will certainly be a difficult and tense row to hoe. In the end, it will be up to you. If secrecy excites you, then you could get a lot out of this connection -- as long as that old feeling of betrayal doesn't well up too strongly within you.