Your SO is right. This is a big deal.
Now, as a disclaimer, when my husband and I married (I was 30, he was 35), I did not want kids at the time, and declared myself as “unsure”, and he was open to having kids (I am now decidedly childfree, and being sterilized tomorrow) but at no time did he or I ever suggest if he wanted one, we could have one anyway. He recognized fully that being with me meant kids were far from a certainty, in fact not having kids was the likely certainty.
To me having kids is not a compromise between someone not wanting kids, and someone wanting kids. Not only is that unfair to the children, but I think many people underestimate the impact kids have on your entire life, and your relationship. Is he still really going to feel that way when he comes home from a trip after months and instead of spending a few fun days relaxing with his girlfriend/wife, he comes home to a house full of kid toys, noise, their schedules, their priorities, and so on? When every time he talks to you it is about the baby, or the kids? Some people thrive being parents, and love it. But this guy is giving you very clear messages, in both words and actions, he is not going to be one of those people. You cannot go into this thinking seeing his baby will have him fall in love and change his mind. Because honestly, I can refer you to many people I know who may love their children, but would not do it over again, who do not like parenthood and it all it came with at all. It is dangerous to assume no one could ever regret having children.
At 30 you are young. Most of my peers have had children well into their 30s and even 40s, so there is no real reason due to age alone you would not be able to have children at this point, or for the next several years. I recognize you seem to be okay if your body does not let you have kids, but that is not the case right now. If you want kids You better figure that out now, and realize this is a man who does not want kids, and even if he had them to “keep you”, would at best not be an involved father, at worst be resentful. The things you enjoy about your relationship now, and maybe even him, would not be there anymore.