YOU SAID:

i like my girlfriends sister so much that i want to leave my girlfriend for aforementioned sister

INTO JAPANESE

私は私のガールフレンドの姉妹がとても好きなので、私のガールフレンドを前述の姉妹のために残したいです。

BACK INTO ENGLISH

I like my girlfriend sisters very much, so I want to leave my girlfriend for the aforementioned sisters.

INTO JAPANESE

私は彼女の姉妹がとても好きなので、前述の姉妹のために私のガールフレンドを残したいです。

BACK INTO ENGLISH

I like her sister so much, so I want to leave my girlfriend for the aforementioned sister.

INTO JAPANESE

私は彼女の妹がとても好きなので、私は彼女を前の妹のために残したいです。

BACK INTO ENGLISH

I like her sister so much, so I want to leave her for her previous sister.

INTO JAPANESE

私は彼女の妹がとても好きなので、彼女を前の妹のために残したいです。

BACK INTO ENGLISH

I like her sister so much, so I want to leave her for her previous sister.