Well, you are off to a good start, you are communicating. I don't know what the details of the conversations were so I'm not sure what the underlying issues might be. In general some issues that might create tension is trust, infidelity, sexual promiscuity, sexual activity preference, and so many many more... My feeling is that most issues do arise out of some sort of a trust issue. The main issue is that something has happened in your partner's past and one or both of you has an issue in getting past it, therefore tension arises.
Perhaps couple's counseling would help the two of you to talk about, and get through this tension.