What does this mean - is he dating this girl or not?

well lets see, Him deleting the post could have meant one of two things ether he is embarred of his relationship with the other girl or they were dating but something went wrong and he broke up with her and wants noting to do with her. if he said he is secretly in love with you that means he is willing to be open with you so my advice is ASK HIM yourself no offense but thats the most reasonable and most for sure thing to do! i wish you the best of luck!:)