I'm not going to tell my abusive dad about my sister's hospital visit
Why would you not tell him about your sister being in the hospital?
I don't want him to come back into my life because he just brings pain and suffering
You are there for your sibling in a moment that matters. Speaking to others, be it a parent, a friend, whomever who has wronged you should not be your primary concern.
I just don't care to let him bother me. I'm better off this way, trust me.
I think you're probably making the best decision you can for your mental health. It's okay to look out for your own wellbeing in a situation like this.