What is the main reason for Ciel's abortion and how does she react?

Ciel's main reason for aborting her unborn child is that she believes the abortion will allow her to keep the father.... she sacrifices the child for the man who fathered him/her.

Ciel's reaction to the abortion is one of complete withdrawal. Ending the life of her unborn infant serves to unhinge her mind..... in losing the child, Ciel loses herself.