For some people, foreplay (oral, fingering, etc.) is more personal and intimate than intercourse, and it's that level of intimacy that scares them and makes them uncomfortable.
I had a gf back in college that was like this. Fucking she was comfortable with, anything else and she became terrified. Oral just made her feel too self conscious, when my face was down there she had this horrible feeling that I was "examing" her. She had a host of issues that I found out later...
Oak, good luck bor.