Why after so long does my fianc'e/girl friend still not want to have sex?

Hm. a month, five months, six months… Guys I have been waiting a year and five and a half months. It has been causing such incredible amounts of stress. I love this girl and have no intentions of leaving her ever. We have planned our futures together, named our children, set out a path for our dreams. Designed our perfect home. Fought till tears blinded my eyes (of course i try not to let her see that lol) made up. (of course i am always wrong… except those occasional times) We have come so close, so many times. We have been physical so many other ways. (no oral or anal) We have compromised on everything possible. We have been through so much together, and yet she is not ready for sex. We are both virgins there is no background of betrayal. We love each other to the ends of infinity. She tells me she is comfortable enough, and trusts me enough to have sex with me. I ask if i am not attractive enough, and she laughs at me in response and tells me that is definitely not it. She has Dreams about us having sex. But she says she is not ready. Her body tells her yes, but she forces her mind to say no. I don’t understand. She gives me mixed signals, pulling me in every direction. Tormenting me from moment to moment. Some nights i cry myself to sleep, softly of course. I have been patient for this long, and still i wait. But my heart can’t take this much more. My mind is raging with questions. I have even become depressed it feels. What is wrong with me, if she loves me, if she trusts me, if shes comfortable. I know it isn’t because i’m ugly, because it definitely isn’t so. She knows i trust her,I love her, and she is one of the very few people i feel comfortable around. Her dreams indicate the want, her body, and heart do too. So some one please tell me why she isn’t ready?