Pervert

Okay so I’m just coming on here to let some stuff off my chest... well I was at the mall with my sister and her bf, I noticed that he was walking around with a boner and doing the most to hide it, I only noticed because he was like dancing around moving his clothes and stuff & I also noticed that he was looking at almost every girls ass in the store, it only bothers me because I feel like my sister doesn’t deserve that. She is a really good person but that’s not the only thing, he’s abusive towards her, she pays all the bills while he spends the most money to pay other women for nudes (they don’t even send the nudes) he asks for a username to form of payment, send them cash & THEN asks for nudes for the money he sent.

She tells me that she wakes up and catches him lying next to her jacking off to porn.

He goes to work and gets home/ gets mad if there isn’t food made for him or the whole house isn’t clean after his “long day” he works part time, she works full time. I don’t know what to say to her anymore, she doesn’t have social media so if he messages any other girls asking for photos or sexual favors they expose him on Facebook and I call her immediately to let her know, she gets mad at him and the next thirty minutes they are “fine” again but I know it hurts her, she won’t leave him. Should I continue to tell her when I happen to find things out or should I just stay quiet? Sometimes she even blows up on me because she wants me to screenshot EVERYTHING and sometimes I’m busy so I’ll let her know what I saw and hang up well she’ll get mad saying “why even tell me if you’re not gonna give me everything” so many girls post that he is a huge pervert and gets mad if they don’t send nudes, he saves everyone’s nudes and blackmails them if they don’t send more. I get real bad vibes from this guy, he rips her clothes when they fight, I would be extremely surprised if he doesn’t rape her or something. He even sent a lot of people my sisters photos & SHE STILL WONT LEAVE.

Idk what I should do anymore

Edit; my sister knows she always has a place at my house, she has left but it’s a routine she leaves/ starts to drink and becomes suicidal/ other life problems have caused this.