DSis' met her DH after I moved away for uni and we haven't lived in the same town since now quite far so when we visit it is usually overnight or weekend visit. We are 40s now, BIL late 50s. From the beginning he was abusive but she has stuck with him. I have questioned and challenged things about their relationship but clumsily and she was defensive so I tried to stop to not push her away. Things got worse since lockdown and I also realised too late that he eavesdrops on our conversations. Several times when he and I were alone in a room together I felt open hostility from him. I also suspect him of breaking something of mine intentionally and a few other incidents. Over Christmas we ended up having an argument and my sister was so defensive of him and upset with me that I still feel quite shaken by it. We have another weekend together planned and I honestly feel like I can't do it.