AIBU to feel heartbroken that my husband does not want another child?

What you’re fantasising about is just that, a fantasy.

You know from past experiences that child birth, babies and things completely out of your control can alter your predictions.

I’m really sorry that you didn’t get the two maternity leaves that you wanted, but you do have two healthy DC and that’s incredible!

Even if you got pregnant quickly there would be a 6-7 year age gap between your oldest and youngest. The oldest therefore is more likely to be pissed off that mum is too busy feeding the baby to play with her, or host play dates, or drive her to the trampoline park or whatever. Your eldest will be learning to drive when your youngest is in primary school, so they’ll be at different stages throughout their life and maybe that won’t matter and they’ll be best friends, or maybe when your eldest asks for driving lessons and you can’t afford them because you’ve just paid for three lots of school uniforms and school shoes, they’ll be annoyed you had a third.

I get that the desire for a baby can be all consuming, but don’t mix up fantasy and reality.

Gently, OP, you’re doing that classic thing of ‘This time it will be different!’ Vanishingly few people experience the ‘idyllic newborn bubble” you appear to think everyone has experienced but you (my newborn stage with DS was very difficult because of an infected CS scar, no milk supply and FH being made redundant), and it would be completely mad to have another child in the hope that this time you’ll somehow have it.

Combat your fantasies by thinking about your two existing children getting far less of your time and attention, or being jealous and finding the transition difficult. I mean, it’s just as likely an outcome.

Concentrate on all the things you'll get to enjoy with the children you have. Talk to your husband or a friend about how you feel. Neither of you are wrong in how you feel.