YOU SAID:
She went to the party with his boyfriend, his boyfriend went to the party with her
INTO JAPANESE
彼女は彼のボーイフレンドと一緒にパーティーに行きました、彼のボーイフレンドは彼女と一緒にパーティーに行きました
BACK INTO ENGLISH
She went to a party with his boyfriend, his boyfriend went to a party with her
INTO JAPANESE
彼女は彼のボーイフレンドとパーティーに行きました、彼のボーイフレンドは彼女とパーティーに行きました
BACK INTO ENGLISH
She went to a party with his boyfriend, his boyfriend went to a party with her
You've done this before, haven't you.