YOU SAID:
because tonight, for the first time
INTO JAPANESE
今夜、初めてだから
BACK INTO ENGLISH
Because it's my first tonight
INTO JAPANESE
今夜が初めてだから
BACK INTO ENGLISH
Because this is the first time tonight
INTO JAPANESE
今夜は初めてだから
BACK INTO ENGLISH
Because this is the first time tonight
That didn't even make that much sense in English.