Marriage? Children? Can you you help me?

I am 24 years old. My boyfriend is 28 and we've been dating for over 2 and a half years, but I've known him since high school.My boyfriend is at that point in this life where he has a really good job. He has a nice house. He's financially stable and he seems to be going very far in life. But, he's also at that point in his life where he wants to get married and eventually have children. But I, on the other hand, am still in school and I don't feel that we're ready to get married. Even though our relationship is golden and wonderful and fantastic, I just don't think we're ready. After all, marriage is a BIG DEAL because you're promising to yourself, GOD, your future spouse and all those that attend that your wedding that you will do right by each other and be with one another for better or for worst of anything and everything...That takes a great deal of commitment. It's not that either one of us can't commit to each other. It's just that I feel as though..my boyfriend and I's relationship is like a cabinent where the nuts and bolts are screwed in but some of the shelves of the cabinent are not as tightly screwd as others. Hopefully that made sense. Now, I know that every marriage has it's kinks and lose shelves but I WANT OUR shelves to be firmly secured from the ground up. Like I said, it's not a commitment issue nor a trust or loyalty issue. It's just that I don't think our relationship is 100% ready to carried out the ways of marriage. If I could give our relationship a percentage then I'd say we're about 77% ready for marriage but that 23% is just not fully confined and confirmed. I try explaining this to my boyfriend because he's proposed to me TWICE but I just dont think he understands. He has also bought up the fact of having kids and I LOVE KIDS. If I'm going to be a pediatric dentist then I have to love kids...But in all seriousness, I really do love kids to death, but I don't want to have kids. I don't want to tell him that because if you could only see the look on his face when he plays with his nephew or his god son and the joy he gets...you wouldn't tell him either. I am actually contemplating the idea of getting my tubes tied and not telling him so that way whenever the time comes for children it will kinda seem like it's his fault, ya know?? I know it's wrong but... I guess I just need some advice from a you guys. I can totally understand where he's coming from with wanting to get married have have kids. I mean he's 28 years old and he'll be 29 in 2 months so he's not exactly getting younger but I wanna wait at least another 5 years before even getting engaged and at least 3 years after the enagagement before we get married. And as I said about the kids, I don't want any so the tubes might be tied by the time the enagement and marriage even happen.....Do you guys think I'm crazy or over doing it? HELP ME, SOMEBODY!!! I talked to my pastor. I prayed. I talked to my parents and of course I've talked to my boyfriend about everything except the tubes being tied...SOMEONE GIVE MY SOME ADVICE!!! PLEASE!! This is so stressful.