It's time to take a long, honest look at the ways you're each behaving in this relationship, and at the ways that each of you views love affairs in general. You've both been unconsciously acting out old feelings from your past -- traumas you lived through and encoded into your own psyches without even realizing it. Those old traumas are coming up again, asking to be processed and set free.
But that process won't be an easy one, and this period of several years could be difficult for your relationship. Be careful how you treat each other; remember that honesty is always best in the end, as keeping secrets from your intimate partner is hurtful in the long run. Being aboveboard will be harder now than usual; you might both develop obsessive attractions toward other people, because your sexual natures are stimulated now and your potential for obsession is high. Focus on treating each other with respect, first and foremost. It's possible that by the end of this transit, you'll both decide that it's time to let go of each other, but it's more likely that this process of letting go will apply to feelings, behaviors and attitudes that are no longer useful to you.