Oh gosh, I feel your pain... I hate to sound like a jerk but it's nice to know I'm not alone. I also am madly in love with someone I can't have for reasons I also choose not to go into (she also feels strongly for me, but cannot act on her feelings or it would turn her life upside down). I, like you, have also had to sever contact with this person and it can really crush the spirit... especially when I begin to compare every new love interest with this one person whom I cannot ever be with.
I wish you luck... knowing a love can never be really sucks!