My "mess around" buddy

I've been messing around with this ftm guy, and he's really nice but when he was a (s)he when dated once before and back then my mom and I both knew they were toxic then but now he seems a lot better so we've been trying to hang out but my mom said "trans isn't real you if you have a dick you're male and pussy you're female" and then said "people never change" which all in all is bad but I don't know if I should keep messing around with them behind my mom's back because we don't talk in school because of the way he was before.