それじゃ、私のことはもう好きじゃないの？would sound right to me. (あなたはcan be omitted in this case.) Anta is rarely used unless you're furious with someone and want to disrespect him/her.

i'm learning Japanese now, i guess this would be better : それで、私のことはもう好きじゃないですか？（sorede, watashi no koto wa mou suki janai desuka?）