Porn is ruining my relationship - what should I do?

I have been dating this man for almost 3 years, in the beginning, everything was perfect, had sex every night and sometimes more than once during the day!

Just a little after our 2 year anniversary, everything changed. He wasn't the same man

--he'd rather watch porn then have sex, he would wake up- watch porn, go to work, come home- watch porn, eat/shower –watch porn again, then go to bed

Every time I ask him about it he just says “it's nothing, it's an old habit and that I shouldn't take it personal!”

I don't know what or if I am doing something wrong!