How can you desert me?

I have come out to my parents and younger sister about being bisexual and things have played out in a way I never thought they would.  I am dating a transgender guy and they do not approve.  My mother is labeling me as a lesbian and says I am sinning in God's eyes.  My mother doesn't believe in transgender and thinks it is wrong.  I for one have absolutely no problem with it.  I've known I was bi for about eight years now and have never told anyone accept for one close friend, that I was questioning.  I had gotten to the point where I just wanted to be me and stop trying to live my life how my mother wanted me to.  I've known my boyfriend for years now and knew him way before he decided to make the transition.  I liked him back then but was afraid to ever mention it.  It wasn't until recently that I learned he had feelings back then too.  We started going on dates and finally made it official two months ago.  I'm the happiest I've ever been but at a cost.  I moved out of my house to get away from the situation and am doing so well now.  I thought my family would be a bit shocked at first but I thought they would understand and just want me to be happy.  I was very wrong.  My mother says she will never accept me, it's not right, she will no longer be there for me and that she's done with me.  Those words stung like nothing I've ever felt before.  My mom was my best friend and I've lost her during one of the hardest times in my life.  For once I'm standing up for myself and for what I want.  It feels good but it hurts all at the same time.  I am hoping she will come around eventually and things will blow over.  If I didn't love him as much as I do I wouldn't be fighting for us.  I have told my grandma (my mom's mom) and she couldn't be happier for me.  She can't believe my mom is doing this to me.  She wants so badly to talk to my mom but I told her that it would be more meaningful to me if she came around on her own.  I don't need her being attacked right now.  I'm angry and hurt but I would never wish anything bad on her.  I hope that one day she will regret the things she has said.  For now, all I can do is hope for the best.