For many people, perhaps most people, having children is a completion of their lives and they would not truly fell fulfilled without them. However, not everyone feels that way and that isn't necessarily a wrong or selfish choice. Also, some people feel that after so many, they are complete and don't want any more children. That isn't wrong either.
If having children is that important to you, you are going to have to make a choice. At least your boyfriend is being honest with you and telling you what he wants, not stringing you along saying "maybe in a year" or "maybe when we've saved some money." He's saying flat "no." Even if it hurts you, he can't help how he feels any more than you can.
Perhaps it's time to face the fact that you don't want the same things out of life, out of your future together. You don't want someone you're going to have to talk into being a father, do you? You want someone who can't wait to have a family with you. Those men are out there. You mentioned that you've been "off and on" which makes me also wonder if there aren't other issues in the relationship, as well. Just because you've invested this much time in him, doesn't mean you have to invest more. You're only 27, you have time to find the right person you will be compatible with going forward.
Another danger is that he ends up caving and you have a child, but he still doesn't really want it. What kind of father will he be if that is the case? You want him to jump in with both feet. You deserve that and your children deserve that.
Best of luck to you. You have a lot to think about.