Mom issue

Layla • Arab/American Hybrid
I'll try to be as simple as possible about this. 
So basically my mom has been living outside our family home ( I am guessing with her lover who is much younger than her ) for maybe 4 years now if not more. My parents are legally married but she broke our family apart. I don't blame only her I blame my dad too because he's an asshole who doesn't know how to show any affection (even to his own kids). 
The issue is this: my mom is parading around with her young lover all over Facebook and to her friends and is public about it. She does everything for this "kid" who will eventually leave her because she is way older than him. I used to fight with her about not ever being home.. But now it's like whatever she will see. She basically left all of her kids here just to be with someone who is a play thing and using her. 
I know he for sure is using her for money because he makes next to nothing ( she always asks me and my brothers for money all the time but we don't know what she needs it for)
It's all really sad because I have two younger sisters. The youngest is doing well just drowning in her studies however the one who is 22 is lost and very fragile. She has nothing going for her and is never home either - she started cutting herself recently which worries me but I can't do anything.
All of this gives me anxiety where I feel like I can't breathe because everyone relies on me to fix things. I had to grow up pretty fast because of all this and it's so HARD to be going on this way
So to conclude: I think they should get a divorce so at least we have a clear view of our lives. All of us kids are just so confused we don't even talk about it ! Ugh I wish she would grow up...