I'm cutting my relationship with my mom

My mom makes such horrible decisions and I'm so done because this one conflicts so hard with my morals. I know everyone will say "That's your mother". But honestly idgaf. There are some things you just don't do. I know some will say it's not my business and you're right. Its not. But it's my decision to be involved with her. My mom left my dad a couple years back. I was 16 and she just walked out. Didn't give af. She came back into my life wanting a second chance. So she works at a mental health institution. She does pet therapy and there was this boy in and out of the minors unit. He recently came back and now that he's 18 he's been put in the adult unit and my mom has admitted to having a relationship with him. A sexual one.... She's waiting for him to be discharged and he's gonna move out of his dad's house into her house and she's gonna help him manage his Social security check and you can see where this is going..... Fucking no. My mom is 51 years old and had been messing around with this barely legal mentally ill CHILD. O at least hope this didn't start until he was 18! I can't with her and I'm done with her. There are things I simply won't have around me and that's one.