Feeling confused

I grew up with these siblings, dated the brother a little bit but remained best friends after the break up all throughout high school. Well I was really close with his little sister too like I said we all grew up together. I started dating a guy(Tony)my sophomore year. We were all really close or whatever but me and Tony broke up after 3 years of being together. I'm married with a baby on the way so this is in no way jealousy but I'm so concerned about her. She's dating Tony, she's 18 and can make her own decisions, but we had broken up because he was abusive. I ended up in the hospital 3 times due to him messing up my ribs, he choked me on multiple occasions, kicked me through a fence and slammed me on the ground in front of a ton of people at a birthday party. She knows all of this, she witnessed it on many occasions. She's always been like a little sister to me and I do not want to see her hurt but if I say anything they're gonna swear I'm jealous of their relationship. I just can't see why someone would knowingly get into a relationship with an abuser when she deserves so much more.