YOU SAID:

Im going to the next party with him and you

INTO JAPANESE

私は彼とあなたと一緒に次のパーティーに行く予定です

BACK INTO ENGLISH

I will go to the next party with him

INTO JAPANESE

私は彼と一緒に次のパーティーに行きます

BACK INTO ENGLISH

I will go to the next party with him