Confused

Alright, this may be long but I'll try to keep it simple enough. I have an older sister (14 months older) and we've been super close our whole life. It's a stange kind of thing but we also seem to go through similar situations in life around the same time as each other..

She has been with her guy for about 2 and a half years and the relationship is toxic and abusive (has been physical) but mostly emotional from what she tells me. Her guy is schizophrenic and drinks too much and treats her like crap.. I got out of a realtionship that was similar about 2 years ago as well and it completely changed my life for the better!

So, she ended up getting pregnant with him and had a very difficult pregnancy because of him.. She came to stay with me and my bf more times than I can count and questioned why she was having a baby with him... But she always went back and eould be upset that I didn't want to be around him. She has a son now who is soon to be 10 months, and I have a son who will be 7 months on the same day... (We were pregnant at the same time)

Life hasn't gotten any better for her since her little man was born at all.. The guy is terrible.. He doesn't help her, puts her down, accuses her of cheating, super jealous, says bad things about our family etc...

So, at the end of April she ended up leaving for the day to get away from him, went back home after and things got ugly.. I once again opened my door for her to stay and she moved some of her stuff in. My bf and I were getting ready to move for June 1st so we had our son's room full of packed boxes, but arranged it so she could have a space for her and her son. He cancelled her phone so I got her set up with a plan under me. She didn't have any money so she couldn't really help out with meals or anything. I told her I wanted it to be the last time.. That she could stay with us until she found another place.. She said it was done. She spoke with a lawyer.. We went to get more of her stuff.. He was an asshole as usual.. It was just terrible.. He changed the locks to their house and denied her access.

So my bf and I often leave for the weekend to go stay at his parents' place which is about an hour away. The first weekend she came and stayed with us.. My in-laws are amazing! And the second weekend which was mother's day weekend we decided to go and give her the apartment to herself. She was sad that we were leaving but I explained to her that I needed a break from everything. It's very taxing emotionally to watch someone you love go through this.. And I just needed some space. So we left..

We ended up going to my mom's for mother's day lunch on the Sunday and I asked her about her weekend... I could just tell something was up... Long story short, she went back to him... I was so unbelievably upset.. I just don't get it... I felt so used and taken advantage of.. I took care of her.. She really didn't even do much to help out when she was with us and just went back like that. My boyfriend and I were the ones to move her mattress for her even...

We spoke about it when she came to get her stuff and I told her I was disappointed. That I want nothing to do with him at all... I'm done with it. And that I won't take her in like that again either. Which is maybe harsh, but it has seriously happened at least 5 times now..

Now... About 2 weeks ago I was having symptoms and decided to do a pregnancy test. I went to the pharmacy and ended up running into my sister. She was getting a test too. I spoke with her later that evening and asked about the result.. She is pregnant again.. So am I... It was unbelievable.. But I'm just so confused and usure how to feel about it. I love her son that she has already and wouldn't trade him for the world.. But I think she's making a huge mistake having another baby with this guy...

I've told her my concerns and that I'm worried about her.. That she seems all over the place.. She just spoke with her doctor about depression as well... It's just a crazy scenario.. When I try to talk to her she gets super defensive and brings up that I was in a bad relationship too...

Anyway, I guess I just don't know what to do about it.. I'm scared for her and don't want her to feel even more stuck.. What would you do??