There is a disconnect between your daily experiences and your partner's moods and emotions. Somehow, you're out of sync; you have a fantastic day, full of good things happening, and you come home to find that your lover is feeling gloomy and pessimistic -- and you're dragged down. Or, on the opposite side, your lover could have an awful day and feel annoyed by your unfailing good humor, and consciously or unconsciously, they do all they can to pull you down to their level.
As your relationship progresses, and especially if you live together, you find that something in your individual daily routine is in direct conflict with that of your partner. Your lover is living more in the past than you, held sway by some old experiences or hurts that have never really gone away. You live more in the present, and you have the chance to teach them your way of living -- letting go of the past and moving forward. Obviously, this is an important lesson to learn, but a difficult one. When any of us encounters things in our present life that remind us unpleasantly of our past, our instinct is to rebel against it or run away from it, unless we've already done the hard work of processing the past. That is what this relationship is about, in part, for your partner -- facing their past and learning to live in the here and now.