I am 17 and my boyfriend and I have been having unprotected sex for a while can I get Pregnant if he doesn't inside me?

If he is inside you at anytime there can be sperm and you can get pregnant. If you are going to have sex at least use protection. It is careless and foolish not to. Do you want to get pregnant?

AND It only takes one time for it to happen

Yes.

Yes you can, happens all the time, plenty of sperm in the most of the early fluids.
Not finishing inside, only lowers the chance, does not stop it

I see the pregnancy test question, tell us what is happening, have you missed a period ? Done a test ?