"He’s probably just trying to keep his feed limited to his closest friends."
I'd have to go with this as the most likely explanation for why he unfollowed you.
Still, I can definitely relate. A large upvote from a dolphin feels like immediate validation of your work and can be very rewarding from a psychological point of view.
I'm still struggling with my own blog, so my advice might not count for much, but I'd definitely urge you to hang in there, and continue posting great content and network with people whose material genuinely resonates with you personally.
Maybe I'm naive, but I still have this belief that if you're talented and comitted, then you don't have to kiss ass to get recognition for your work.
RE: Being unfollowed by a whale/dolphin feels like shit