The subconscious mind is so powerful. Every experience - good or bad, leaves an imprint on our subconscious. These memories travel with us through various rebirths. And in turn, give rise to our karma in every lifetime. Everything you're experiencing now, is a direct result of something you've already done, caused, or experienced in the past. We re-live experiences over and over again, until we burn the karma and learn the lesson. That's how some people attract negative relationships repeatedly. It's because the experience is imprinted. So every new relationship is basically the same, because the person is already anticipating how it is going to go, based on what they've experienced in the past. They are 'creating' their relationships to be painful because they haven't learned the lesson and instead of introspecting, they're going into another new relationship with the same conditioning. This cycle will not end until the person becomes aware and conscious, and blatantly stops the undesired, repetitive behavior.
Remember, you create your life. So instead of carrying the weight of the past, let go and forgive. Don't hold onto the pain. Free your subconscious mind.