You married Kagaya young. You both were simply children trying to please your families and keep the bloodline fresh. It started out with simple touches, you would heal the infected parts of him, his scrapes and bruises, and you would eliminate his disease. He became grateful and began to dote on you in return, showering you with affection and love, whether it was platonic or not it didn't matter.
What started out as platonic though, quickly turned into genuine romantic affection. He stopped relying on your healing abilities once you became pregnant with the quintuplets, not wanting to have you exhaust yourself trying to save him. He would do anything for you and for the five children you gifted to him. He will go to great lengths, just to see you smile once more.