What should I do????? What would you do?

I am 14 years old and am certain that I am bisexual. Now I have a kinda- girlfriend who is also bi. She is one of my best friends, and so I hang with her and text her a lot. My whole family is homophobic though. At least, my mom and younger sister are... My sister actually tried to talk me out of being bisexual when I tried to come out to her. I let her think she won, because she wants to be exactly like me and I didn't want her pretending to be bi, thinking that she's cool. I have nothing against anyone, I just didn't want my sister faking a sexuality. Anyhow, my mom has been insinuating that there is something more going on with my friend and I (which there is). My mom said she would do something, I forgot what, if I hooked up with another girl. Whatdo you think I should do????? Thanks!!!!!