Atheists; do i have to tell my moms bf.....?

what happens at the doctors? we have no relationship + trust or respect, yet she and him think i should and now hes asking what happening at the doctors but i want to keep my information "personal" and they may kick me out of i refuse to ell..and my mom may tell too cuz shes a dog to him and always blabbers her mouth to him things i feel. so please..what should i do?=)