I have a friend who is an avid diver and he's sick on every single dive. He's never overcome it in 30 years.
Myself, I don't get seasick and enjoy surge. I've even been on a rolling dive boat during high wave conditions where most everyone but the crew were barfing. I knew that it could be contagious and so looked away. Easier said than done when the man next to me barfed into his towel. I swallowed hard and looked further away.
Oddly, the only time that I feel a very slight nausea is standing on a dock or a boat that is not discernably moving.
Always the extreme exceptions. Maybe I should have said it gets better for most of the people who continue on.
I have to give it to to your buddy....not sure if I would still be getting on a boat after a while. Being seasick is no fun. I use Scolpamine patches, I'm sure he's tried everything? With those I can eat, laugh, use the head downstairs all while rocking back and forth.