I'm not sure I have any helpful advice as I night weaned DS at 14 months. His reaction was much the same.
Maybe at his age you need to create a narrative that you can use to explain the change and work through together to ultimate weaning. Like a countdown to when he's a big brother with no night booby or something along those lines.
Have you read Pantley's No cry sleep solution books? She has one for toddlers that might have helpful suggestions.
Good luck