This shouldn't be a big deal. It's my social media, I can do what I like but...
I loathe ex-BIL with every fiber of my being. For lots of reasons, many directly related to how he treated SIL as well as how he behaves/behaved around the rest of us etc. During their break up, he said and did a lot of things that were absolutely unacceptable. One of those things, which is actually probably less serious in the bigger scheme of things, is that he sent DH a series of messages in which he accused DH and I of being abusive, toxic and manipulative. He also said and implied all kinds of other things and admitted some of his abusive behaviour to SIL but attempted to justify it with comments like, "it's the only way to get her to shut up" or "she needed to be taught a lesson." Needless to say, he has never apologised or acknowledged how deeply inappropriate any of this was.
While he has finally moved out of their (rental) house, he is present at SIL's a lot for lots of reasons I won't go into here. So we do see him. Also over Christmas, SIL asked for him to be included in certain family events for the sake of the DC. Obviously, we attempt to be civil and polite.
BUT, I can't stand it and his attempt to pretend we're all one big happy family drives me crazy (disproportionally probably). He is on my social media commenting on things (with lots of emojis which just makes me want to vomit), or actively engaging in our family WhatsApp group. I just want to delete him off, at the very least, my facebook/instagram etc but based on his behaviour previously, I think it might blow back on SIL. I've accepted I can't take him off the WhatsApp group.
Is it fair for me to do this knowing that it could be very bad for SIL and his relationship with her?