YOU SAID:

Have you been dating anyone other than me lately?

INTO JAPANESE

あなたとデートしている私以外の誰か最近か。

BACK INTO ENGLISH

Recently someone other than I have a date with you?

INTO JAPANESE

最近誰かがあなたとデートがある私以外ですか。

BACK INTO ENGLISH

Recently someone is dating with you than I do.

INTO JAPANESE

最近誰かが君とデートするよりもすれば。