[JackOffJill]

Yeah like everyone else said, you really need to tell the cops and your parents. If you need support in doing that, maybe go to the school social worker. I am sure that they would help set up the meeting for you to tell your parents and from there the next step would be to tell the cops.
At some point you do need to tell your boyfriend. This is not something that you can hide from him- it wouldnt be fair to either of you.
Once you have talked to everyone you can start looking at all your options- look at the pros and cons to each one (keeping the baby, having an abortion, having the baby and giving it up for adoption). ultimately, the decision is up to you on what you do- no one can tell you what to do because it is your body--as long as you can deal with the consequences.
But please go to the cops. Even go to the cops first and then with their help tell your parents. you really need to get this guy out of the school system before he does this to someone else.