I understand you're disappointed, but I think it's very important to do this TOGETHER. I have known so many people whose families have been damaged permanently by one partner deciding to have a baby over the objections of the other, and I don't want to see that happen to you.
Imagine if you were happily living your life believing that you would someday have another baby, and then one day your husband came home and said cheerfully, "Guess what? I had a vasectomy today!" You'd be devastated, right? You'd feel it was very unfair that he'd made a decision that would affect you and your family forever, without your agreeing to it, even though he knew that you wanted something different. Well, it would be the same for you to tell him, "Guess what? I'm pregnant!"
Now, if your pregnancy was REALLY an accident, that would be different--similar to your husband becoming infertile because of chemical exposure in the workplace. He wouldn't be justified in being mad at you for that. But if you PURPOSELY get pregnant when you know he doesn't want you to, he has every right to feel manipulated and betrayed.
It's not that his opinion is more important. His opinion is EQUALLY important. A marriage is supposed to be about two people working together, not one person scheming to get the other person to give her what she wants.
From what you've been telling us in various threads, your husband has not been very assertive. His behavior up until now has made it easy for you to hear what you wanted to hear. I think it would be helpful to talk w/him about that and tell him, for instance, that you expect him to be responsible for buying and using condoms, and that when he doesn't use one you will take it as a sign that he's willing to conceive. You could also offer to involve him in charting so that he's aware of when your fertile times are. Also, make sure you understand correctly that what he's saying is, "If we accidentally conceive again, I am willing to have another child rather than an abortion." not "It's okay if you want another child, just don't tell me when you're trying."
MrBecca used to say he didn't ever want children, back when we were first dating. We discussed it many, many times, and I got really frustrated and despondent, because I wanted to spend the rest of my life with him but I also wanted to be a mother, and I didn't know how that was going to work out. I prayed about it (and I don't mean, "God, please change his mind!" but "God, please guide me to make the right decisions.") and I waited patiently and tried not to bring it up too often. Eventually he decided he was willing to be a father someday, and then I prayed and waited some more, and finally he decided he was ready to start TTC. It was not easy. BUT IT WAS WORTH IT.
I know it's hard not to get something that you want so much.
But try to relax, work on having a loving partnership, and trust God to bring you what you really need.
And I saw pics of him and his sister. You could just see the love in his eyes for her...they basically despise each other now....LONG story....which is why I don't think he is worried about giving ds a sibling. I on the other hand love my sister dearly and couldn't imagine life without her......
or abstain. Dh has this funny sense of when I O. He can normally tell a day before! Not to mention that I get incredibly horney..more than normal 
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