What you have to understand about your mom is that she was raised a certain way and has beliefs imprinted on her. Usually, our beliefs are given to us by our parents, and those beliefs don't change until they are challenged. Your mom's belief about sexuality has probably never been challenged before. Just have a sit down and explain your feelings with her, hopefully she will be able to understand or at least make an effort since she's your mom.
A quick story for you: I have this guy friend. He was raised hardcore Christian and taught that homosexuality was a sin and you would go to hell for it. Well, his parents split up several years ago, and his mom told him and his sister that she was a lesbian and she now has a partner (who she's been with for a few years now). My friend really struggled with this because of what he originally was taught to believed, but eventually came to terms with it.
His situation is similar to what your mom will have to go through, and hopefully she will come around, but you really need to have a serious talk with her and help her explain WHY you feel the way you do and ask her for her support and love.

Good luck.