Each of my children have several only children, and nicer, happier, more well adjusted, confident children you couldn't meet.
One mum did tell me that she would have loved another child and asked her son once would he like a sibling?, ......he answered he'd prefer a puppy, which they promptly got.
The most important thing is a happy, healthy mother.
Don't spoil this time beating yourself up with guilt, it solves nothing IMO.
Continue to enjoy this time.
You sound like a great mum and a sensible one.
He didn't step up the last time and isn't even prepared to put in the tiny effort of educating himself,........ yet he would like you to carry a baby for 9 months and possibly go through this again?
Not a chance would I do it.
You need to firmly put yourself and your health first, that is the best thing for your family.