should i marry my girl friend?

a girl likes me more.. i too find it interesting.i left dating with other girls boz of her.we find it entirely amusing when we are together..but we are aware that we both are from different caste and status. if we get married we both will be happy but sure not both of our society.. i told her that we will be friends till any of us get married first, but she insists for the contact even after both of our marriage. she tells that i should maintain the same type of relationship(even sex)after my marriage with other girl.. then it will be a betrayal to the girl whom i get married..and ofcourse to the guy whom she going to marry..is it possible?