I think it's nuts to blame a kid (in this case, Katya's partner back then) for her mental health, her suicide, and her twin diseases of addiction and epilepsy, both of which can be deadly.
And I don't know if any of you know Katya's partner personally-- I don't, and so can ONLY speculate as to what kind of person he is. In the documentary, he comes across as measured in his emotional reactions, a bit distant maybe but kind and appropriate with her (at least on camera) and is reluctant to throw ANYBODY under the bus, including Katya. He does not go on about her drinking, which was probably awfully problematic, I assumed out of respect for her or maybe he didn't even know the extent of her disease.
People seem keen to form a person's entire character around a couple of misguided or simply immature online comments. He's still young, and doesn't seem like the a-hole people seem outright determined to paint him to be. I've read hyperbolic comments online on another site and elsewhere about how his partner "deserves someone better." Seriously, how can people even claim to know? We know so little. Tired of the character-bashing. Personally I wish him and Hye-Jin Cho well.