Bf lied about watching porn?!

*WARNING: long message*
So sick of hearing lies.  In AUGUST my bf and I argued about masturbation because we were in a long distance relationship.  I was cool with him doing it, I just wanted to know when.  I was not, however, okay with him watching porn.  The thought of him getting off to another girl(s) makes me sick and completely insecure.  He promised me he would tell me if and when he masturbates.  He also told me he would never watch porn again.  Since then, he hasn't said a word about it, so naturally I figured, he must not be doing it.  I even ask him if he has and he says no.  One day he left for work and I was using his computer.  I go to google chrome and as soon as I start typing, PORNHUB comes up.  So I open up his history.  BAM, loads and loads of porn sites visited.  Recently too.  It frustrates me because a) he broke his promise about watching it b) we literally have sex almost every day, sometimes 3-4 times a day and c) I can't help but feel jealous.  Like an idiot I actually believed him when he said he never finds other girls attractive since he's met me, and that I'm all he ever wants.  When I calmly approached him about it; he brushed it off like nothing was wrong.  I told him that I was considering breaking up with him because of the way he lies (by omission), and because he just doesn't seem to care that I'm hurt, ever.  Overreacting? Thoughts?