Mom Still Sleeping With Him..

My mom and dad split when I was about 14, I’m now 23. My dad was emotionally and physically abusing my mom throughout their 25 years of marriage. My siblings and I grew up witnessing this but my parents always laughed it off. I no longer speak to my father, he’s toxic to be around and I don’t want to be apart of any negative energy. My mom and dad talk on and off every few months, not too sure why.. it’s a weird situation. My mom had me do something on her phone earlier on today and I came across some sexual messages between the two. This isn’t the first time this has happened. She has told me that she’s going to her sisters place tomorrow night which I know is untrue because my aunt works night shift almost 7 days a week. She’s also done this in the past.. she’s lied about where she’s going her and my father would be ‘together’. I’ve also come across messages where they ‘plan’ everything. Where they’re going to meet, what time.. EVEN plan what my mother says to me if I ask her anything