I do absolutely understand how you feel... but all younger siblings feel pushed out by a new arrival, and when that new arrival is there 24/7, that will be worse. The usual rule of thumb is to make a huge fuss of the older child, so they don't resent the younger. In this case, that's exponentially more important.
It's worth remembering that a loving and positive relationship with a sibling is one of the best things you can offer your child. Supporting and promoting that early is in the new baby's interests, too. Siblings are going to be there when you and your husband are gone. How close they are, and how much they support one another, is partly fluke and personality - but very much partly parental management, too.
Really do think that it's off for your DH to say his priority is you and baby. His priority should be the three of you. If, god forbid, you were to pass away, and he remarried... would you like knowing he could tell a new wife that she and her newborn, and not your child, were his priorities? At such a vulnerable time for any child, let alone the child of a relationship that no longer exists - the arrival of a child from the one that now does? I hope that was a strictly time-sensitive statement on his part, but even then it's tone deaf as hell. This is a very tricky stage to navigate, for him and his son. He needs to be aware of that.
There's a book called Siblings Without Rivalry. It's very good.