Deeper Concerns Than Lasting Love
I think right now you may need to get some priorities and focus on them. If there is a possibility that you are pregnant, then you have deeper concerns than if your love will last until you are married.
It'a About the Child
Bringing a child into the world is a very difficult thing, especially when you're little more than a child yourself. Please don't be insulted, I am 25 and feel the same way about myself. You need to do some real hard thinking about what you want for your life, and what you want for your child's. You can't be selfish at this point, this isn't about you, it isn't about your love, it's about what kind of life you will be able to give this child.
Seek a Counselor
I don't envy you your position, it involves a lot of growing up, and doing it fast. You need to speak to your boyfriend, and the two of you need to see a counselor.
There are places that specialize in teen pregnancy, (Planned Parenthood, for one) and can help you explore alternatives or help you to prepare for a child if that is what you want.
Straining the Relationship
Now as to your relationship, girl, this is definitely going to put some serious strain on it. Your boyfriend was right when he wanted you to focus on you, and that in itself speaks volumes about his character. You definitely need to talk about this with him.
He May Feel Trapped
In this day and age a lot of stress is put on who decides the future of a child, but I got news for you girl, it usually takes two to make the little guys, and he has as much right regarding the future of the child as you do. Steel yourself for some resentment, he may feel "trapped" or backed into a corner. This is natural, but get your back up and don't try and take full responsibility because his reaction displeases you. You have to understand that this will radically change his life as well. In whatever the two of you decide, make sure it is for the best; the best for you, the best for him, and most assuredly, the best for the child.
Your love may have to play second fiddle to this for a while, or it may be the thing that gets you through this. Your first priority should be to this child.
Have Sex Responsibly
Now if you're not pregnant, (and for everyone's sake involved) I hope you're not, then get to your local Planned Parenthood and learn about contraception. If you're going to have sex, then have it responsibly. There are many methods out there to choose from, and you need to protect yourself from disease, and prevent pregnancy. Explore this even if you are pregnant. I can't begin to tell you how it has saved me. I wish you the best of luck.