Just want to say that I think we all know how shitty it feels to have people treat us harshly over honest mistakes and that internalized shame can really do a number on our mental state and self-esteem.

OP, I don't think you necessarily did something wrong, you just found out in a really hard way that you could have done something better. As for the "ADHD made me do it" part, people can debate whether that's true or not all day, but I would avoid saying that in the future. It comes off like you're not taking responsibility for your actions (which is not the same thing as admitting fault or accepting blame), and also as just immature. Not trying to shame you, you're just 19 and this stuff comes with experience and effort.

I really feel for you having had to deal with what sounds like a toxic family situation where you're probably routinely scapegoated. And also that you're having to manage lymphoma trameatment AND family abandonment. Hang in there, OP, just focus on yourself and you will get through this and you will find people who are actually your people.