Sex addiction/porn

My fiancé demands sex as "one of his needs as a man". He watches porn more than (what I think) any one does.. Even while driving from what he's told me. **** I'm not against porn in a relationship, I don't personally watch it but I've told him before that as long as it's on his phone/computer & not mine, I don't care.****
Lately because of finding out that he's lied to me repeatedly (other sexual partners/ drugs/ other various bs), and being disgusted by it, we haven't been having sex. He now purposely watches porn, right in front of me.. Even while we were at my mother's house & apparently his grandmother's.. According to her. 
He's told me as of today that he has thought about cheating on me because I've been failing to meet his needs. This is the same person that for the past four years, has told me he loved me & for the past year, wanted to marry me. I'm at a loss as to what to do, we're fixing to move in together & be married. 
Am I overreacting or should I run.?

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