A feeling of distrust will surface between you in this life, stemming from the fact that in a past one, you let this person down in a big way. Whether this betrayal was due to your own negligence or rebellion or it was completely out of your control, it left a scar on your partner's soul, one that still hasn't healed. This time around, they'll have a hard time relying on you, even if you're perfectly willing and able to create a stable bond, because subconsciously, they don't want that past-life betrayal ever to happen again.
Whether they realize it or not, they have responded to those old past-life wounds by creating security structures in this life that make them feel safe, perhaps in the form of relationship 'rules' or by sticking to safe, traditional paths toward their goals. Your influence in their life, then, can be a good one, because you'll be there to shake things up for them and remind them that the safe path isn't always the right one. This won't be an easy journey, however, for either of you. Because this person will enter your life for an equal but opposite reason: to teach you how to stay grounded and appreciate a conservative approach when the situation calls for it. Working out your differences will require lots of communication and cooperation, but if you grow to care about each other enough, you can make it work.