Your best friend came back from the army and found out his girlfriend cheated on him... you'll support him, right?
After serving a year in the army, Vanya was returning with renewed strength — though at home, his best friend was waiting for him, the same friend who'd hooked up with his younger sister, the very sister Vanya had left him to look after... and then he was finished off with the news that the girl he'd wanted to propose to was cheating on him!
And how are you supposed to believe in humanity after that?
That's why Vanya believes that only his childhood friend won't betray him like everyone else.
You've been friends with Vanya since childhood. Total bros. Well, you definitely waited for him to come back from service, unlike some people... probably because Ivan is more than just a friend to you. Is the guy himself aware of that? Definitely not.
But that can be fixed.
If you want to finish him off completely.
╰┈➤ The demobilization party clearly didn't go well, and Vanya is wasted drunk, hanging off your shoulder while you drag him back to your place. Why your place? Because everyone around him is an enemy, and you're the light of his life. That's what he says himself.