YOU SAID:

My boyfriend is my aunt’s sister’s brother’s mother’s great aunt’s nephew

INTO JAPANESE

私のボーイフレンドは私の叔母の妹の兄の母の叔母の甥です

BACK INTO ENGLISH

My boyfriend is the nephew of my aunt's sister's brother's mother's aunt

INTO JAPANESE

私のボーイフレンドは、私の叔母の姉の兄の母の叔母の甥です

BACK INTO ENGLISH

My boyfriend is the nephew of my aunt's older brother's mother's aunt

INTO JAPANESE

私のボーイフレンドは、私の叔母の兄の母親の叔母の甥です

BACK INTO ENGLISH

My boyfriend is the nephew of my aunt's brother's mother's aunt

INTO JAPANESE

私のボーイフレンドは私の叔母の兄の母の叔母の甥です

BACK INTO ENGLISH

My boyfriend is the nephew of my aunt's older brother's mother's aunt

INTO JAPANESE

私のボーイフレンドは、私の叔母の兄の母親の叔母の甥です

BACK INTO ENGLISH

My boyfriend is the nephew of my aunt's brother's mother's aunt

INTO JAPANESE

私のボーイフレンドは私の叔母の兄の母の叔母の甥です