He actually screwed the kid... He never deserved anything like that. No wonder Guts turned into a battle-hardened warrior.
Donovan's death was a well-deserved slice of revenge. Ever since Gambino got his leg cut off, his bastardous side became more apparent to the point of giving Guts an existential crisis at the age of 11 and telling him that his only father figure sold him to a rapist. Damn.