Question: 1990s book about loner who fantases that girl he meets at drama class is girlfriend and kills her

Asked by oogybear on Fri 24, Feb 2012 01:34pm :

The guy narrates the first part and explains his girldfriend is
killed/missing. She narrates the second and it becomes clear she didnt even
know him. A third part makes it clear he killed her but is denying or
blocking it. Maybe at oxbridge college? All help remember this book
gratefully received!