I guess YMMV on what you consider “realistic,” but if we’re talking about realism as a synonym for believability — in that how a character expresses grief is realistic to what we understand about them — I’m unsure what, if anything, is unbelievable about how Kirk grieves Spock’s death in TWOK.
They don’t make em like they used to.
Indeed they don’t
Honestly, it was just Shatner. I was just never moved by his acting, anywhere. Loved his comedy!
Limiting discussion to series. Serieses. Shows!
Watches Spock die and processes his final words, struggles to maintain his composure while giving a beautiful eulogy at the memorial, connects with his son for the first time and discusses how he’d never faced death until now, and then remembers the wisdom that Spock was giving him on his birthday.
Or how the crew of Big D grieved the loss of Tasha Yarr, with renewed waves of grief whenever something triggered a memory of her years later.