Why does my boyfriend still watch adult rated XXX videos behind my back?

We have been dating for over 2 years now and I still find him on those sites... I don't understand why he feels like he has to do that. Is it me? Am I not enough for him?
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Ok I can see the whole addiction thing, but it bothers me to the point to where I don't know how much more I can handle it, it has lowered my self esteem significantly! And he knows it, we have talked about it numerous times but still no change, I don't want to leave him, I have never had feelings for another like I have with him and I don't want to lose that! What do I do?
Why does my boyfriend still watch adult rated XXX videos behind my back?
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