I guess you can see your partner's point of view in this -- he honestly believed that he wasn't risking an unwanted pregnancy by having unprotected sex. He knew he isn't ready to be a father.
But this isn't his decision anymore, and you should not let him talk you into doing something you don't want to do. Ultimately, you may have to choose between your relationship with him, and your chance of having your own child. In your situation, if you wanted a child in future, either with him or with someone else, and were unable to get pregnant again, I suspect you would be very angry and resentful. You need to think about your future, and what you want. Nothing is ever guaranteed -- if you do go ahead with an abortion, there is nothing that guarantees your relationship with your partner will survive anyway. You might end up hating him, or you might drift apart. If you go ahead and have the baby, you may find yourself a single parent and have to face the resentment of someone who is trapped into being a parent, but if having a child is important to you, then you need to make that choice. He is only thinking of what he wants right now -- it doesn't seem like he is understanding how you are feeling about this.
What I am trying to say is that there are no promises -- a lot of men do come around once the baby turns up, and a lot don't. You might even go off your partner once you have a baby. Or the two of you might decide to make a go of it, but somehow it doesn't work out. But all of that can happen whether you have the abortion, or whether you have the baby. The pregnancy, whatever you decide, is going to change the relationship between you and your partner.