I don’t know if this perspective helps.
I wanted kids desperately for as long as I can remember and tried to go through a process to have them alone. It became clear that wouldn’t work because of a previously undiagnosed medical condition. Aged 35 I decided I’d focus instead on finding a good man and a good partnership if I was lucky enough to get that opportunity.
I met my now husband aged nearly 39, he was a little older. He was very ambivalent about having children by that age (for sensible reasons) and then various difficult things happened to him and his family that meant it felt unwise to push it. We did try after we got married but it didn’t work out. We are both sad we didn’t meet younger and have children but we have a good life.
One of the hardest things about the situation for me is that my younger sister has kids - so I have a niece and a nephew. They are great but since she had her second our relationship has changed for the worse. We’ve never been super close but have had some great times together especially in the ten years before she had kids and even when she had her eldest. Now she will only do things with me and the kids, she’s disappeared into her family and I feel like a spare part despite my best efforts. My parents are sad about it and of course love her and the grandkids but understand my position too.
There are no guarantees that giving your child a sibling will make their life better. You can’t guarantee cousins or grandchildren. Not all siblings are able to or willing to share care for elderly parents equally (I’ve seen this in my husband’s family) and it can cause tension. No one deserves any child let alone more than one. It’s not always better to have any or more. I’d have been massively grateful for just one in the end and in many ways came to see it as the best option given the world we’re in.
I do love my sister but I think either of us would have been ok being an only child. My mum has always been very against the only child scenario and me and my sister have both always thought that’s odd, what’s the big deal? My husband has an only child niece, some of my friends have only children. It’s complex and there have been compromises but they are happy families overall, have more money, flexibility and can give more to their other relationships and the world around them.
Society’s conditioning makes it hard for us all and I do think you are projecting your own feelings in saying your existing child will suffer - they won’t and they won’t necessarily gain from having a sibling.
If your husband has messed you around that’s really hard to come back from however and it’s very hard to judge a marriage from the outside.
But I have learned the hard way that in an uncertain world sometimes being grateful for what you have and making the most of that (if you judge you have a relationship worth saving with a man who truly loves you) has a lot to be said for it. It’s perfectly reasonable not to want a second child or any child particularly in certain circumstances. It’s not reasonable to mess someone around though life can be hard to navigate and people can change their mind.
Don’t know if that helps at all because I am not in your shoes. But try to separate the different elements of this, and consider what’s most important. Compromise isn’t always a dirty word but you do need to have space for both your feelings and those of your husband.