You shouldn’t cut him on on behalf of your mother. Maybe I’m projecting here because I’ve got a shitty dad, but I reckon your dad’ll give you a reason of your own to cut him off soon enough. He’s starting a new family with the affair partner and doesn’t have time for you? The new affair partner doesn’t like that you call her the “cheating slag” on your weekends with dad. Really there are plenty of reasons likely to pop up, no need to use your mothers excuse.