Would this make me selfish?

I feel like I know the answer already and I hate it. But my dad has depression too and has outright told me he would kill himself if I did. What about my mum and sister? I care about them so much. Half the reason I’ve stayed alive for so many years is because I don’t want to hurt my family.

But I’ve hit a point where I’m in so much pain and I feel so disgusted by the world, that it would almost be unfair to live my whole life only for the sake of other people. Why should I live if I’m not even doing it for myself?

But if I die knowing that they’re at risk of losing my dad too, and knowing that I’m dooming them to an even bigger amount of misery and grief, that makes me a really selfish f*ck. How can I possibly die with that information in my head? I’ve hinted to them that he’s said this to me but obviously they don’t expect it’s going to be an actual problem at some point. They’ve said themselves if they thought I was gonna do it they’d get me admitted to hospital so I can’t tell them the full extent.

But I just don’t know what to do? What would you do in this situation?

It also really doesn’t help that my dad has sort of been competitive about suicide in the past. He’s literally said things like “I’ll beat you to it” and stuff like that. So I feel like he honestly would try even if it was just a threat at the time.

(I can’t believe I’m asking this but do you think it would be totally out of line if I wrote a note and pinned it to my shirt, warning of this, so when the police find my body, they can do something about protecting him/my family??)