I think it really depends on what your view of being happy...

You could be happy both ways:
1. Leave him... you will find someone else to love and this one will love you back... You will be happy and start a family together like everybody else.

2. stay beside him, be his "friend"... at the end, he may not choose you, but you think you loved for your love. Everything is worth it! You will be happy that you were at least in his life once. 曾经沧海！

well, I think most people are just ordinary ones... I would choose 1.

Good Luck! Getting over someone is not that hard...