My father keeps breaking my trust

As-salamu alaykum. My dad has always been narcissistic, physically and verbally abusive and used to drink a lot. He’s stopped drinking, but the other problems are still there. He has spat at me, thrown things at my face, threatened to hit me, and tried to kick me out whenever things didn’t go his way. We go through the same cycle: I stop talking to him, he apologises, I forgive him, and then it happens again. Right now I haven’t spoken to him in six months, even though we live under the same roof. I’m tired of forgiving because nothing ever really changes. Recently my mum asked me to check her phone and I saw a flirtatious message on his phone. I looked through other messages and won’t go into detail, but they were inappropriate for a married man with grown children. He acts pious and religious in public, yet he behaves this way and mistreats his own family while treating strangers with great respect. I won’t tell my mum because she’s already suffered so much and I don’t want to hurt her more. Maybe she suspects something, maybe not. I just feel emotionally exhausted and burdened by what he’s doing. I have no one I can comfortably tell - it’s embarrassing - and sometimes I find myself tearing up for no reason. I’m sharing this because I needed to get it out. If anyone has advice about setting healthy boundaries with a difficult parent while keeping family ties as Islam encourages, I’d really appreciate it. JazakAllahu khair.