Before I say anything, note that I'm an atheist and things I say might offend you. But this is the reality.
From what you've described, I see no possibility of your family ever coming to terms with your decisions and actions that are not in the strictest adherence to their ideas, values and faith. I can't imagine the mentality of "my child is doing something I don't want - shame and disownment." That's not how you treat a person, a human being and a daughter. Make no mistake, harbor no illusions - this is Islam on a daily basis. Islam doesn't need to be taking down skyscrapers and killing infidels to cause harm. It can cause a mother to threaten to disown her daughter simply because she fell in love with a non-Muslim. It can cause you to think that you have no choice but to make a choice between yourself and your family.
As definite as it might be in your situation, I suggest you to appeal to your family one more time - as a daughter, niece and sister. Explain yourself and your feelings. If your family can somehow, anyhow understand - keep in touch. However, if they can't, move away, leave them behind and follow your feelings and your heart. Both you and your partner are mature, responsible adults with great prospects in life and I warmly and kindly suggest you do the right thing. Start living your life independently of your mother, your father and ultimately - independently of Islam. You've been a loving, caring, loyal family member for years, but obviously, that won't make you happy and isn't making you happy. That won't allow you to live your own life. Start being a loving, caring, loyal person in general, loving, caring for and loyal to people who deserve it. People who value you and treasure you for who you are as a person and an individual, not for who you are as a Muslim. Have a long, meaningful conversation with your partner, explain the situation, let him know what would this all means for you. If he understands you, respects you, loves you and recognizes what you need to sacrifice for your relationship - be with him, be free.