Considering the above, there is obviously something causing this problem, otherwise it couldn't be there. It's either due to a condition that has remained true throughout your life, or it's because of an action--something somebody else (or yourself, leading to somebody else's actions) did, therefore causing your "phobia" (for lack of a better word) of sex.
So it's something your boyfriend is saying. Before I make any assumptions, let me ask the following:
- Any childhood events that could POSSIBLY lead to anything?
- Have any close friends that were abused/raped?
- What exactly does your boyfriend tell you (that scares you to death)?
- How open were your parents with you about sex?