I'm going crazy and I need help

I’m 26 years old, and my whole life until a couple of months ago some people in my family abused me physically and verbally, and my partner did too. Mental illness runs in my family; I grew up with a schizophrenic and narcissistic father. I stopped talking to my dad sometime ago but recently he was diagnosticated whit cancer , also I live alone. My partner also has mental health issues but is taking medication, and now he’s not as abusive toward me anymore. I’m supposed to be patient with everyone, and I always go out of my way to help everyone. For some reason, now that no one is hitting me or telling me I deserve to be treated badly, I’m suffering a lot. It’s as if my mind were scolding me every day and saying the same horrible things they used to say to me, and every day I think about killing myself and how I could disappear without anyone knowing or killing myself. I’m having a lot of trouble concentrating on my work, and I’ve already missed out on many job opportunities because I just sabotage myself. I feel like it’s already too late for me and that I’ve already broken down, and I don’t know how or when. When I tell people this, they think they’re just excuses to justify why I don’t work or why I’m late for everything, but no one believes me. They make me feel like I’m exaggerating to get attention, and sometimes I think about killing myself to prove to everyone that what I’m feeling really is real.

It also doesn't help that I recently became addicted to marijuana and cigarettes again. My dad is a drug addict, and I grew up in an environment where that was considered normal. The first time I used those substances was when I was 4.