My sister is dating a guy that is clearly abusive (posted briefly before about him) they have only been dating 8 weeks and they argue every week, sometimes more, and I don’t mean bicker I mean huge fights/swearing telling her to never speak to him again etc. After 2 weeks he told her he loved her 
every time they argue they are back on the next day. It’s abit draining listening to it as she will say how awful he is how he screams in her face etc but then back together the next day. I tried to be supportive but it’s only been 8 weeks, I couldn’t not express my judgement when she said she was going to introduce him to her son after around 5/6 weeks. They’ve continued to argue constantly, 2 days in a row over the last few days. She called to talk about it which she always does so it’s hard to stay out of it and said they had an argument where he was screaming and swearing at her, texted her 50 times and constantly calling. When he couldn’t get through to her he called her son 
I’m biting my tongue massively as I don’t know why a man she’s been seeing 8 weeks has her sons number. And worst yet is involving him in the arguments. She said he said he was going to beat her up, I asked her to clarify that was his actual words (because she’s been doing a thing where she says he said something then I will quote it when they get back together and she will deny he said it and make out like I’m twisting it) she got annoyed at me and said “I’m going to go as I’m not having another argument!” And slammed the phone down on me.
This is a man that’s also going to get her name tattooed on him apparently! And she said she would do the same if he does. He’s told her all his family and friends hate her. I honestly don’t know what to do in this situation as she takes it out on me, am I right to be concerned?