Love always demand sacrifice. One can enjoy martial happiness if he/ she have a kind of self-sacrificing or putting the interest of other person before his own interest. If ur love goes beyond flower, chocolates, hearts, candy boxes then ur love is going to make in the long run. Unconditional love is given without defining any parameters. Those who love unconditionally always want the best for their loved ones. They will allow them to be free to seek what will truly make them happy.
When u love someone unconditionally then such things like give n take never arises. Its always about being happy with ur loved one. And when we start putting our partners interest before our own interest then this will create a positive cycle & it will encourage ur partner to do the same, therefore builds a truly happy relationship.