"He is between you and me."
Translation:Él está entre tú y yo.
I was confused about esta vs es. But I googled it. The sense I got was that "esta" is used when you are describing a situation whereas "es" is used when you want to describe a general ongoing attribute of the subject. He is nervous - El es nerviosa (he is generally nervous) He is nervous - El esta nerviosa (he is nervous at the moment)
Yes, normally the ordinary subject pronouns are used after prepositions except for 1st and second person where "mí" and "tí" are used.However certain prepositions like "entre" use the ordinary subject forms "yo" and "tú". You need to look up the prepositions that do this, a few are: según, excepto, menos, salvo, incluso.
What says that? That is incorrect for two reasons: (1) There is no de that attaches to the preposition entre (and even if there were, it would have to attach to BOTH ti and mí) and (2) the preposition entre, as ricrog posted above, is exceptional in that it takes subject pronouns (yo and tú) instead of prepostional object pronouns (mí and ti). (Also, note that mí has an accent and ti does not.)