This is hurting me. I don't know what to do?

So a couple of days ago I told my mom I was in a long distance relationship with someone I don't know. And it seems like all she did was think of the negative and talk bad about his culture. It had me thinking and second guessing but he made me realize that I wasn't thinking overall. And she don't believe in long distance relationships and it's been almost 7 months with him. Shouldn't that tell her something? I know we're 3 years apart and a million miles away but that shouldn't determine how we feel. And I feel like my mom is holding onto me like let me fall in my own butt. Like I'm so mature for my age yes I get I'm technically a minor and he's technically a grown up but come on 3 years? My father and her is 10 years apart and my stepdad is like 6 years older than her. She just absolutely doesn't believe in me and his relationship. And just think it's completely odd and label him as a possible threat or predator. And it kinda hurts me cause my mom is like a bestfriend and I'll believe her before I believe myself... I really care about him and he makes me so happy he's all about me and he told me he wants to marry me like you know how hard it is for a boy to want to marry you? Nowadays you can't just find that and to her it maybe just internet but we still been through so much... what to do?
This is hurting me. I don't know what to do?
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