It's two traumatized people who have to go to therapy. I was also surprised to read it the first time, but Jay has a low tolerance for frustration and he has volatile reactions to things (beating people, and destroying their lives because they don't do what he wants) so this makes sort of sense.
It doesn't make it right, but the way he is acting out, kind of makes sense. Especially since Jay saw the suicide scene (too realistic), Taemin didnt reach the phone when he could have answered, and he also wanted to die before, so Jay did the asshole move of: if I kill myself and you feel guilty, you would live right? Because Taemin lived because of the guilt for his family (repaying his family) so now he would "repay" him.
Jay is volatile to the max, that combined with the fact that he normally acts out his feelings in impressive shows (without processing them well) led to this. At least both of their psychology is consistent.
Taemin doesn't need this shit, and he needs to process everything himself. I just want them in therapy...in my lala land because it, probably, will never happen.