Thanks for bringing your question to JustAnswer.
I can imagine how confusing it must have been for her to withdraw from intimacy once she started to care for you.
Your friend clearly has problems with emotional intimacy, but not sexual intimacy. This is unusual, but not unheard of.
Sometimes people who did not bond with their parents in infancy, for whatever reason, can never really feel close to another human being---sex is as close as they can get. Feeling an emotional attachment is, on a very deep level, frightening to them. They pull away when someone tries to love them.
Another possibility could be a history of sexual abuse in her childhood. When the trust of a child is broken through this kind of abuse, they can grow up unable to trust anyone, if they never get treatment to resolve the early abuse.
And of course there is one more possibility... she liked having relations with you but isn't looking for or wanting a long term relationship. She has asked to separate and you have to honor that request.
It is probably best to not try to be a support system for her, as your own feelings are involved. It would be too much for you to handle when she gets involved sexually with someone else.
It sounds like you want a relationship, not just someone to have sex with. Perhaps next time it would be worth considering to put the emotional intimacy before the sexual intimacy.
If she has either of the two disorders I mentioned in the beginning, she would need professional help (and a desire to work on her problems). Neither of these is something that a friend can help with....the effects run too deep, and are too painful.
I hope this helped! Please click ACCEPT if it has, or reply if you need more information.