Sometimes it has to do with how the baby's mouth is shaped or structured. Your nipple is different from his thumb. So is a bottle nipple. I don't know anything about "tongue sucking" in the womb. And a lot of babies like their thumbs a ton more than they like a pacifier. Why do you blame yourself for this? It is unfair to yourself to do that.
I always feel bad when I read on here that it affects women so hard to not be what they "consider" to be successful at nursing. There are so many other things in life to regret, and how long you nurse shouldn't be one of them. Look, you nursed one child for a long time. Just because the next child didn't take to nursing doesn't mean you failed in any way. And pumping can be absolutely miserable. I was not able to pump at all - tears would flow down my cheeks and I never got more than a teaspoon full out.
When your children are teenagers, the LAST thing you will be thinking about is that they would be a better kid if only you had nursed. PLEASE put this out of your mind. You are smarter now and know that you will not miss your child getting dehydrated again, that no matter HOW this child gets milk, you will keep him or her from having to go through that. THAT is what matters.
It turned out that my own son has a submucous cleft palate and with a compromised structure, sucking exhausted him. Nursing is hard work for a baby. It is easier to drink from a bottle's nipple. That's why my son was so much happier when I weaned. I didn't know it - it didn't matter to me why - but after we had all those tests, we all knew.
I don't beat myself up for this, for supplementing so that he got enough in him, for switching to a bottle several months later, and neither should you. Accept what IS, and move on. Since you successfully nursed one baby, I'll bet you can successfully nurse another one.
Dawn