An old conflict in a former lifetime will make itself known again in this one, albeit in a subtle way -- and in fact, that subtlety will make the issue all the more difficult to deal with. You won't recognize or remember the issues that led to conflict between you; they're too deeply buried in the layers of your subconscious minds, and all you'll be able to connect with now will be those vestiges of feeling, including anger, resentment, betrayal and aggression. You aren't likely to be openly aggressive with your partner, however.
Your style will tend much more toward passive-aggressiveness, letting them know you're upset by sending subtle, indirect cues that will likely annoy them to no end. They will take the much more direct approach in this relationship, really letting you know when they're upset with you -- but pushing you to open up and have it out with them won't work, either. They won't appreciate your emotional sensitivity, however, and you could reach some sort of stalemate -- again, without even connecting with the base of the problem, which is this lifetimes-old betrayal that was never healed or resolved. The best way to resolve this difficult karma once and for all, then, will be to decide whether this relationship means enough to you to tackle the issues. If so, then make a commitment to be as open yet gentle with each other as possible. Talk out your feelings of suspicion or hurt rather than acting them out or turning them into simple betrayal. You're likely to find that you have less to be upset about than you thought.