The purpose of a relationship is not to be loved perfectly, or forever. It is not to have our every whim and wish met and fulfilled. It is not to be completed, or to have our minds and hearts fueled by the hormonal stimulation we think is the feeling of love. The purpose of a relationship is not the Universe's way of saying "you're worthy, and here's someone to prove it."
As human beings, it is difficult for us to grasp the concept of time. It always feels like we will have tomorrow until it is too late. We put love off for future dates, fully confident that we can spend more hours together and be more loving later; blinding ourselves to the fact that life is unpredictable and mostly out of our control.