I have had this same issue with my mother. i think your dad just doesn't understand this illness and feels helpless. he can't fix this thing and he might even wonder what he as a parent could have done wrong. I know that it where my mom's denial sprung from. there is no quick fix for this but as long as you have your mom and boyfriends support i guess that is all that matters. your dad not accepting your bipolar doesn't mean he doesn't accept you and his denial is his problem. just don't let it get you down, i'm sure he will come around one day.