between you and me.
It is a prepositional phrase. Pronouns at the end of prepositional phrases should be in the objective rather than than the subjective case, " me " rather than " I. "
If you reverse the order of the two pronouns, your ear will tell you that " between you and I " is wrong:
between I and you. (That doesn't sound right, does it?)
between me and you. (That sounds all right. We sometimes get the idea from our fourth grade teachers that we have to mention the other person first in a phrase like this. It may be more courteous to mention the other person first, but it is not wrong grammatically to mention yourself first.)
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