I agree that being separated from your newborn is very hard. I love my sons and cherish the time with them.
When they were infants, I would adjust my own life to what was appropriate for their ages. Sometimes, being a parent requires that we sacrifice something that we want to do because it would not be right for the kids.
I simply do not think that a newborn baby belongs on a cruise ship. And to avoid the separation anxiety, hold off on your cruise until the child is older. There are plenty of alternatives to a cruise vacation, all of which are better suited to the presence of a newborn.
I know that parents will rationalize it to suit their own needs. That's fine. But on a message board, if the question is asked, I am going to voice my opinion that it is not a good idea to bring the baby along on the cruise.