Such a circumstance is torture, to be sure. Unrequited love/desire is a nearly universal experience, which makes it relatively easy to get over. But to be in a relationship where the love is mutual and includes desire to make a life together, but the other does not welcome or share the natural desire for physical expression of that closeness--that can't help being painful.
Sometimes one has to choose. For most of us, I think, the choice would be to move on. Let the beloved be a friend, but renounce the physical desire that is rejected, and keep searching for an other with whom you can build a more complete relationship, one that does not call for giving up so much of who you are.