Best Friends Brother

So I've like my best friend Marys big brother. For like two years and just this past summer I find out he likes me too. I whent over to Mary's he asked me out. And I say yes of corse. But I did not tell my mom because he's like three years older than me. When she found out she told me to break up with him but I didn't. When she foud out she said that she dissappointed in me and all of that crap. But the thing that makes me fill glity for is me and my mom are really close. It will be 7 weeks sence we seen each other and my mom will not let me go over to Mary's house with him there. I do not know what to do to seem him or how to stay with him and my mom be ok with it. Hep me please.