9 months old is a "growth-spurt" time.
He is hungry.
He needs to be fed... breastmilk or Formula, which ever you are using.
A baby's intake levels has to keep pace with the growth and development of a baby... if not, they will be undernourished.
He is not spoiled. A baby needs comforting and bonding. These are crucial for the development as well. And for brain development. And for proper development.
For the 1st year of life, a baby's PRIMARY source of nutrition is from breastmilk or Formula and they NEED to be fed ON-Demand. 24/7 day and night. Solids and other liquids, are NOT their primary source of nutrition. This is per our Pediatrician.
And yes, "separation-anxiety" is NORMAL. It is a part of NORMAL development... if a baby does not go through this, they are then not developing normally. So, your son, is only doing what a baby does.
I recommend the book: "What To Expect The First Year", and "What To Expect The Toddler Years", which you can find at any bookstore or online.
Your baby needs to be fed. He is hungry. That is what babies do. Especially at growth-spurt periods. EVERY 3 months or so, a baby goes through growth-spurts. It is NORMAL.
You need to feed and comfort your baby.
all the best,
Susan