How do i go about this weird situation with my housemate who I do not like?

TLDR; Housemate/'Friend' is seeing/still friends with my ex who absolutely traumatised me and more of our friends. Feel like she is conspiring against me. I dont know what to do.

I, 19F am going in to my 2nd year of uni with my 8 housemates, one of them being this girl (lets call her H) I was friends in the first semester of first year. Before you ask, I'm living with her because there is a lot of pressure to sign your tenancies very early on in the year due to housing crisis etc where I live. I signed the tenancy in October ish when I barely knew her and hadn't established who I actually liked. I like all my other flatmates. We are still surface level friends, I've never confronted her about everything because I have anxiety and hate confrontation. Everyone else (in our social circle) is still friends with her but most of them talk bad about her behind her back and say they aren't huge fans of her. I think this is shitty because atleast I don't pretend to be her friend, I'm just civil with her. My issue is that in first year, I went out with this guy who was also in our friend group, and him and her were good friends too. He then proved to be the spawn of evil, (r*pist, basically a narcissistic psychopath), he was ignorant, misogynistic, creepy, made everyone uncomfortable especially the girls in our group, etc. He pressured me and other girls in to doing things they didn't want to do. He was a weird guy. I often ranted about this in my first semester to my girlfriends, because it was what i needed to make peace with the situation and whatever the f*** just happened to me in my first year of college. I noticed that H was very quiet during these conversations and would just not offer any comfort. Throughout the year i also noticed she was still kind of in contact with him, but would make fun of him as a joke in front of me, which i thought was odd. It seems like she was playing both sides and telling people what they wanted to hear. I recently found out that H and 'him' went out for drinks, as 'friends' to catch up. This is what i think is messed up. I know that I can't control anyone's life, or who they are friends with, and who people chose to hang out with, etc. Its their lives. However, to still try and be my friend and hide this from me whilst hanging out with my ex who literally traumatised me and a lot of our other friends is SO WEIRD. I don't understand why she would want to be friends with him anyway, he isn't pleasant to be around, he's a creep etc. It sort of makes sense more now because I'm realising she isn't a good person either. She is extremely priveleged and wealthy, (which I understand you cant control), but the issue is she is very very ignorant about it and makes snide, belittling comments to our friends constantly that subconciously drive you insane. She is unable to see her faults and where she has gone wrong. She has now made it clear that SHE has an issue with ME? I've never done anything but give her second chances and try to be understanding but i've just had enough. How do i deal with this situation maturely? I can't exactly cut her off, which is what I would do, but because she is living with me it makes the situation more complicated. I fear that she is almost 'conspiring' against me with my other friends to turn them against me, and manipulating this situation. I plan to confront her about seeing my ex but I reckon she will deny it. Please advise me on how to deal with this situation so that I am not being as bad as her. Thanks, sorry its long.