You share similar security needs, or at least complementary ones. You may have experienced similar past-life traumas, which led to the particular security needs that you have in this life. Perhaps you both lived in grinding poverty in another life, so now you're both attuned to working hard and ensuring that you have enough money in the bank and food on the table to feel comfortable; or maybe you both experienced some form of emotional betrayal in the past, so now you both work to ensure that your relationships have a firm foundation of trust and intimacy.
Whatever your prior-life traumas might be, you're both willing to do what it takes in this life to avoid living through those same experiences again, and you'll work together toward this end. You may even do so unconsciously, without having to spell out your feelings or your intentions on this level. This will make both of you feel quite comfortable together. You'll know almost instinctively that if other factors are in place -- affection, love, goals and so on -- you'll be able to create a positive, mutually supportive connection that can last far into the future.