To be honest, I think that you are being unreasonable, but you have a lot on your plate, so it is understandable.
Tbh, I much prefer older kids to newborns (and I did even when I had one baby and one older child, it's just that I was stuck with the baby because he was little and defenceless and needed my love and care all the time - I missed my older one so much when she was out and about with DH, who was doing a brilliant job keeping her entertained when I couldn't). If your DP finds it easier with the older ones, that would be understandable, esp if you are bf, so there is less he can do anyway.
If your DS was the only one, I am sure DP would be besotted and at your side all the time. But he isn't - it simply isn't comparable to the situation your DP was in when he had his first DS. You can't neglect the older kids, who he already has a bond with. The bond with the baby will come - my DH barely had any with my second for ages as he was entertaining number one, but they are awesome now at nearly a year.
This is your second for both of you, so neither of you have been pulled in two directions in the same way before. With a second (or third etc), the baby dynamic can be tricky if you have one at a different stage. You often divide and (attempt to) conquer and it can feel like everyone's life has been made worse and you don't see your partner much for a while. It does pass, you just need to try to find ways to keep everyone inside the circle where you can as much as possible.
You will find your rhythm. Have a hug. It will get better.