I would share with your boyfriend. If he really loves you, he will be supportive of you during this time and help you to come to a decision that is best for the both of you. Also, if you abort without telling anyone, including your boyfriend, he may continue to expect sexual relations, and you'll have a hard time coming up with an excuse about safety if he isn't aware of the pregnancy now. And if he doesn't love you and he's just in it for the sex, it's important to know that ASAP!
Then, if the two of you make the decision together early on that the best scenario is to abort, then you can get that done without letting your parents know. Just bear in mind that once you do make that decision, if that's the way you go, it's something you'll live with for the rest of your life - wondering how things would have gone otherwise, etc. Not to say that you'll necessarily regret - but you'll always be wondering. So make certain in your mind that it won't be regret before you make a final decision that way.
If you and your boyfriend want to try to keep the baby, try to work out a "plan" - how will the two of you live and support yourselves to the best of your ability? What might you need help/support from your parents with? Then approach your parents and let them know of the situation, but with a plan in mind as a reasonable adult. They will probably have a bit of a shocked reaction at first, but once they see that you are acting as an adult in the matter, they will probably be more than willing to offer you what support they can. I know it can be embarassing, but most parents just want to see what is best for their child and they will be more helpful than you think in these matters.
I once thought I might be pregnant - I was about your age and I was very inexperienced, also. Luckily, I was very close with my mother, and so she was the first person I talked to, and we didn't talk to my father about it. We found out shortly after (I believe I may have started my period the same day I talked to her) that I wasn't pregnant. So also be aware that the test can be wrong, especially if you have inconsistent cycles. Stress can cause the cycle to be late, and sometimes that throws the test because you are not in the part of your cycle that you think you might be. I had a negative test, but that doesn't mean that your "positive" tests might not be wrong.
May the best of luck be with you...