I'm not judging your actions, but using coitus interruptus (penile withdrawal) is not responsible for a permanant couple. Whatever the outcome of your pregnancy, you need to get on regular birth control, something which can be arranged if you chat with your doctor.
I feel that it wasn't really logical for you to say that you would keep any future baby after your abortion; you can't predict the future or your feelings, although I understand why you made such a presumption. Your partner deserves a worthy say in the whole matter and you should take his views into consideration, although the final decision will always be yours because it is your body that is occupied, not his. The outcome of the pregnancy should be your decision ultimately, after considering the pros and cons of keeping this baby and your and your partner's thoughts.
You have three choices: keep the baby, have an abortion, or give the baby up for adoption. If you are leaning towards not keeping the baby, you need to think which of the remaining two choices (abortion and adoption) you are more comfortable with. Abortion is costly in the US, but keeping the baby is even more so.
I don't think it is fair to bring a baby into an environment that would not be ill-backed economically, loving, attentive, cared for, and dedicated by (a) parent(s) of a sound mental state. Since I don't know the extent to your economic situation, I can't affirm my opinion on your situation, nor would I want my personal morals to affect your decision in any way. Do
you think it would be fair to raise a child in the environment it would be in if you keep it?
There is still a lot of social stigma attached to a second abortion when there shouldn't be. I'm not going to pretend I agree with your previous choice of permanant birth control - it was careless - but you are being a responsible individual for wanting to deal with the issue in the best way possible, whether or not that means having another termination.
My final advice to you is: talk your opinions over with your boyfriend. What will he do if you decide to keep it? What is different about the circumstances around this pregnancy than your previous one which was not long ago at all? Can you cope mentally and economically with raising another baby? Where do you see yourself in ten years and where would you like to be in ten years: do either include another child? Make sure your choice is best all round and try not to regret it - you will've opted for it because it's the best thing.
Kypros.