Marrige

hello, my name is XXX, i live in westbengal, my age is 25, i am in a relationship with a girl, but the problem is she is my maternal uncle's daughter. we love each other and want to marrie. is it possible? i know in hindu socity this is knwn as a sin, but it is true that i love her very very much.....we also knw that this is not possible in hindu society, but we still love each other very much. please guies tell me what to do?

me>my mother>my mother's 2nd elder brother>girl's father