So Konstantin's having a quarter-life crisis. He's having a really bad quarter-life crisis. As Arkadina's son, he associates his self-worth with his creative potential. He's not meeting his own high standards, and lives in understandable fear of his mother's disapproval as well. "She's never read my play," he tells Sorin, "but she hates it already" (1.24).
Yup. When we meet K-man he's the textbook definition of a Gloomy Gus. And his crippling despair only gets more crippling.
This inferiority complex bleeds into his relationship with Nina. When he pulls the kind of nutty (and definitely melodramatic) move of shooting a seagull as a way of showing Nina his pain, she's—understandably—creeped and grossed out.
But he just attributes her coldness to his play's flop:
"You look at me with that cold look; you're always on edge when I'm around. It started that night my play was such a howling failure. Women never forgive failures." (2.87)
(Nah, bro. It's because you shot a bird. That's just deeply odd.)
Konstantin probably learned this little tidbit from Arkadina, whose criticism of his play was merciless. Like his mother, his need for encouragement and praise runs deep.
Konstantin's relationship with his mother is made more complicated by their completely divergent tastes. It's that generation gap thing. Your parents like classic rock, you like hip-hop. At the beginning of the play, Konstantin's all about experimentation. "We need new forms," he tells Sorin, "and if we can't have them, then we're better off with no theater at all" (1.30).
He absolutely despises the trite, moralistic melodramas that Arkadina performs in and openly criticizes her old-fashioned tastes. At the end of the play, however, he's come around to a different way of thinking. Sure, he's still not into the cloak-and-dagger stuff. But he's searching for authenticity:
"The more I write, the more I think it's not a matter of old forms and new forms: what's important is to write without thinking about forms at all. Just write and pour out whatever's in your heart."(4.155)
It's interesting that this discovery immediately precedes the arrival of Nina—as though it's some incantation. She is, after all, in his heart.
Well, he certainly doesn't seem to have a fear of guns or suicide. 1) He kills the seagull for no good reason, 2) he shoots himself, 3) he threatens to shoot Trigorin, and 4) finally succeeds in killing himself.
And why? We don't think it's just about Nina. Sure, that whole business is upsetting him—but it's Nina plus his mother plus his dying uncle plus the success he still hasn't quite found. Plus, most importantly, the psychological distress that keeps him from coping with all this.
Insider info: Chekhov was acquainted with Darwin's ideas of survival of the fittest, and even explores some of them explicitly in The Cherry Orchard. How can Nina withstand the death of her baby, the loss of her love, and the failure of her career? She may be tweaked out but she has an underlying emotional strength. When, in Act 4, she tells Konstantin that the only thing that matters is keeping going, keeping on believing, he simply can't understand her:
"I don't believe, and I don't know what my vocation is. You've found your way in life, you know where you're heading, but I just go on drifting through a chaos of images and dreams, I don't know what my work is good for, or who needs it." (4.177)
These are the last substantive words we hear from Konstantin… besides "Mama would get upset" (4.181). He's just not equipped to deal with the disappointment and uncertainty that constitute real life.